user75: I've stumbled upon this article a while ago, and I've also seen refutations for the Muzio Gambit (Joseph Kling & Bernard Horwitz - Chess Studies on Endings of Games). I'm wondering what other gambits are proven to be unsound.
Edit: I'm looking for refuted gambits in the strict sense of the word, followed by proof. Even though a gambit might be playable against someone who doesn't know its refutation, the gambit is still considered refuted if it is proven that the side who initiated the gambit loses in all variations worth looking at against best play. So yes, I'm looking for scientific proof.
Also, if a database of almost all games played in a particular gambit shows that the side that initiated the gambit wins almost all the time, this doesn't mean that there isn't a way for that gambit to be refuted, it just means that if there is a way, most people haven't played it.
Above everything, I'm looking for material to learn from. An article that says that Vasik Rajlich or someone else has used a computer cluster and came to a conclusion regarding a certain position, how will I benefit from it if there is no proof? (And please note that that King's-Gambit-busted-by-Rajlich article was in fact a Chessbase April Fools' joke!)

user-1: First of all, to refute a gambit, we need to analyse all the lines to a [forced] win. For example, the Latvian Gambit will result in all lines ending with a material advantage for White able to guarantee a win.
However, for the Muzio Gambit, there is no such proof. Black will eventually have to give a knight back to reduce White's initiative, so there is no proof at all.
EDIT: I ran a bunch of games through Stockfish depth 22 with the Muzio Gambit, and Black eventually loses the knight and the position reaches equality.

user15223: The Damiano Defense, also known as the five pawns gambit, is practically refuted. You can find the details on the Wikipedia page. The key line is:

e4 e5 2. Nf3 f6? 3. Nxe5! fxe5? 4. Qh5+ Ke7 5. Qxe5+ Kf7 6. Bc4+ d5 7. Bxd5+ Kg6 8. h4 h5 9. Bxb7

After which Black cannot stop Bxa8 with a decisive material advantage for White.

user2839: Here is an article that describes a way to compare (and refute) chess openings.
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2415203

user3890: I believe there are a few gambits completely solved, that is, analyzed up to positions that either the material advantage is enough to guarantee a win or this win is achieved by means of technique (if the final position is not directly checkmate). The only one that I know a proof of, however, is the Latvian Gambit:
[FEN ""]
1.e4 e5 2. Nf3 f5

The Spanish analyst Alejandro Melchor provides two very insightful .pgn with what he considers to be the refutation of said defense. Here you may download the first one and here you may download the second one. He also wrote an appendix.
They both are deep in calculations and very detailed, if you ever want to play perfect chess against this gambit, then good luck. Even if a gambit is "refuted", not many know these lines and the ensuing complications. This makes almost any gambit, refuted or not, completely playable (provided you are not facing a super-GM).
P.D.: I had to upload the files via a third party, I hopes it's not inconvenient, since I don't know if it's possible to upload files directly via Stackexchange.

user2001: A gambit can be proven to be unsound by using a modern chess engine. Having said this, I would like to mention a comic gambit, known as the Fred defense:
[FEN ""]
1.e4 f5 2.exf5 Kf7 3.Qh5+ g6 4.fxg6+ Kg7 5.gxh7 Rxh7 6.Qg4+ Kh8

White has picked up 2 pawns. In return, the black king has done an artificial castle and black's pieces are ready to develop and kick the white queen around the board. The next plan for black is to launch an attack on the white king and catch it before it has time to castle. Also, the plan is to firmly grab the center, which will restrict the development of white's pieces. To theoretically refute a gambit is one thing. To refute it while sitting at the board is a totally different game altogether. That is why gambits are so much fun!

user70: Many gambits are unsound. The proof is told by the number of these played at the highest levels of the game.  So, if you don't see the Blackmar-Diemer gambit at top tournaments, you can assume that its disadvantages outweigh its advantages.  The King's Gambit is one famously busted opening.
That being said, we're not top players. Most of us can't beat the players who can't beat the top players.  I'd wager, charitably, that 75% of the moves we make are wrong, technically.
In short, they're probably all playable.  As always, if you're going to take chances, book up first.  Understand the opening, know the main lines.

user94: As long as chess can't be calculated from beginning to end, it is very hard to scientifically prove an opening to be refuted (aside from lines that leave you with such hopeless situations like a bare king against king and rook, of course).
If you are satisfied with a less scientific proof, I'd say gambits are even less so refuted. In my opinion, nearly all gambits are playable, as long as you won't play it against a superhuman database/program or a world champion. In a practical sense, probably no gambit worth of having a name is refuted in the sense of not being playable. Even if a gambit is widely considered unsound and often results in a worse position, it might contain enough steam to give your chess skill ample opportunities to overpower your opponent.I even remember a game where I suffered terrible against the BDG because I didn't find any refutation over the board. I only won because my opponent terribly misplayed the late midgame, but from the opening point of view he should have won the game.
So my answer is: No gambit I know of is refuted to the degree of being unplayable.

75: <p>I've stumbled upon <a href="http://www.jeremysilman.com/chess_bits_pieces/110103_blackmar_dmr_gmbt.html" rel="noreferrer">this article</a> a while ago, and I've also seen refutations for the Muzio Gambit (Joseph Kling &amp; Bernard Horwitz - Chess Studies on Endings of Games). I'm wondering what other gambits are proven to be unsound.</p>

<p>Edit: I'm looking for refuted gambits in the strict sense of the word, followed by proof. Even though a gambit might be playable against someone who doesn't know its refutation, the gambit is still considered refuted if it is proven that the side who initiated the gambit loses in all variations worth looking at against best play. So yes, I'm looking for scientific proof.</p>

<p>Also, if a database of almost all games played in a particular gambit shows that the side that initiated the gambit wins almost all the time, this doesn't mean that there isn't a way for that gambit to be refuted, it just means that if there is a way, most people haven't played it.</p>

<p>Above everything, I'm looking for material to learn from. <a href="http://en.chessbase.com/post/rajlich-busting-the-king-s-gambit-this-time-for-sure" rel="noreferrer">An article that says that Vasik Rajlich or someone else has used a computer cluster</a> and came to a conclusion regarding a certain position, how will I benefit from it if there is no proof? <strong>(And please note that that King's-Gambit-busted-by-Rajlich article was in fact a Chessbase <a href="http://en.chessbase.com/post/the-chebase-april-fool-s-prank" rel="noreferrer">April Fools' joke!</a>)</strong></p>
 -1: <p>First of all, to refute a gambit, we need to analyse all the lines to a [forced] win. For example, the Latvian Gambit will result in all lines ending with a material advantage for White able to guarantee a win.</p>
<p>However, for the Muzio Gambit, there is no such proof. Black will eventually have to give a knight back to reduce White's initiative, so there is no proof at all.</p>
<p>EDIT: I ran a bunch of games through Stockfish depth 22 with the Muzio Gambit, and Black eventually loses the knight and the position reaches equality.</p>
 15223: <p>The <a href="https://en.wikipedia.org/wiki/Damiano_Defence" rel="nofollow noreferrer">Damiano Defense</a>, also known as the five pawns gambit, is practically refuted. You can find the details on the Wikipedia page. The key line is:</p>
<ol>
<li>e4 e5 2. Nf3 f6? 3. Nxe5! fxe5? 4. Qh5+ Ke7 5. Qxe5+ Kf7 6. Bc4+ d5 7. Bxd5+ Kg6 8. h4 h5 9. Bxb7</li>
</ol>
<p>After which Black cannot stop Bxa8 with a decisive material advantage for White.</p>
 2839: <p>Here is an article that describes a way to compare (and refute) chess openings.</p>

<p><a href="http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2415203" rel="nofollow">http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2415203</a></p>
 3890: <p>I believe there are a few gambits completely solved, that is, analyzed up to positions that either the material advantage is enough to guarantee a win or this win is achieved by means of technique (if the final position is not directly checkmate). The only one that I know a proof of, however, is the Latvian Gambit:</p>

<pre><code>[FEN ""]
1.e4 e5 2. Nf3 f5
</code></pre>

<p>The Spanish analyst Alejandro Melchor provides two very insightful .pgn with what he considers to be the refutation of said defense. <a href="http://www.filedropper.com/leton1" rel="noreferrer">Here</a> you may download the first one and <a href="http://www.filedropper.com/leton2" rel="noreferrer">here</a> you may download the second one. He also wrote an <a href="http://www.filedropper.com/apend" rel="noreferrer">appendix</a>.</p>

<p>They both are deep in calculations and very detailed, if you ever want to play perfect chess against this gambit, then good luck. Even if a gambit is "refuted", not many know these lines and the ensuing complications. This makes almost any gambit, refuted or not, completely playable (provided you are not facing a super-GM).</p>

<p>P.D.: I had to upload the files via a third party, I hopes it's not inconvenient, since I don't know if it's possible to upload files directly via Stackexchange.</p>
 2001: <p>A gambit can be proven to be unsound by using a modern chess engine. Having said this, I would like to mention a comic gambit, known as the Fred defense:</p>

<pre><code>[FEN ""]
1.e4 f5 2.exf5 Kf7 3.Qh5+ g6 4.fxg6+ Kg7 5.gxh7 Rxh7 6.Qg4+ Kh8
</code></pre>

<p>White has picked up 2 pawns. In return, the black king has done an artificial castle and black's pieces are ready to develop and kick the white queen around the board. The next plan for black is to launch an attack on the white king and catch it before it has time to castle. Also, the plan is to firmly grab the center, which will restrict the development of white's pieces. To theoretically refute a gambit is one thing. To refute it while sitting at the board is a totally different game altogether. That is why gambits are so much fun!</p>
 70: <p>Many gambits are unsound. The proof is told by the number of these played at the highest levels of the game.  So, if you don't see the Blackmar-Diemer gambit at top tournaments, you can assume that its disadvantages outweigh its advantages.  The King's Gambit is one famously busted opening.</p>

<p>That being said, we're not top players. Most of us can't beat the players who can't beat the top players.  I'd wager, charitably, that 75% of the moves we make are wrong, technically.</p>

<p>In short, they're probably all playable.  As always, if you're going to take chances, book up first.  Understand the opening, know the main lines.</p>
 94: <p>As long as chess can't be calculated from beginning to end, it is very hard to scientifically prove an opening to be refuted (aside from lines that leave you with such hopeless situations like a bare king against king and rook, of course).</p>

<p>If you are satisfied with a less scientific proof, I'd say gambits are even less so refuted. In my opinion, nearly all gambits are playable, as long as you won't play it against a superhuman database/program or a world champion. In a practical sense, probably no gambit worth of having a name is refuted in the sense of not being playable. Even if a gambit is widely considered unsound and often results in a worse position, it might contain enough steam to give your chess skill ample opportunities to overpower your opponent.I even remember a game where I suffered terrible against the BDG because I didn't find any refutation over the board. I only won because my opponent terribly misplayed the late midgame, but from the opening point of view he should have won the game.</p>

<p>So my answer is: No gambit I know of is refuted to the degree of being unplayable.</p>
