It did exist but no one is sure what it was.
The making of such was split between different orders and each only knew how to make the next step in the chain.
It was delivered via tubes and could be "thrown" towards the enemy.
Some of those were man-portable, other were ship bound.
Sometimes, you could find it in jars.
The best guess is that it was a petroleum compound but the exact formula is lost.
Source:
John Julius Norwich's history of Byzantium in three volumes.
The below images comes from the 11th century Madrid Skylitzes manuscript.
history.stackexchange.com/users/103/Sardathrion - against SE abuse
Greek fire was used by the Byzantines, often on their war boats, as an incendiary to enemy vessels.
The formula likely consisted of some mixture of naptha, sulfur, and niter among other compounds.
This was basically a Byzantine napalm and was effective at sea because the fire could continue to burn (due to the underlying subtances being highly flammable and not strictly water soluble) even with some water hitting it.
The byzantine war boats fired the ignited substance under pressure allowing some distance to be reached.
history.stackexchange.com/users/18/Seth Rogers
The greek fire certainly did exist, there is a sufficient number of evidences supporting that, including drawings like this one:
It was apparently some flammable substance that would be hurled towards enemy boats to ignite them, definitely not an explosive however.
The exact formula is lost so you will only find some guesses as to what it might have been.
history.stackexchange.com/users/43/Wladimir Palant
It was pitch/tar and oil that was ignited and sprayed if my memory serves me correctly.
It may have had other ingredients (saltpetre, sulphur?) to the mix but it was essentially pitch/tar.
If dynamite existed at that time I doubt they'd have bothered with such a messy and dangerous substance as pitch/tar!
history.stackexchange.com/users/1600/spiceyokooko
I am Greek, so I know something about such things.
Greek Fire was an early form of napalm that was used as a naval weapon because it could burn on and in water.
history.stackexchange.com/users/2292/aea2o5
What was Greek fire?  I read in my history book that it was a flamethrower. But in certain fantasy movies it's been portrayed as something similar to dynamite. What was it dynamite or what? Did it even exist?
What was "Greek fire"?
history.stackexchange.com
<technology><byzantine-empire><weapons>
history.stackexchange.com/questions/160
history.stackexchange.com/users/16/Daniel says Reinstate Monica
It was a flammable substance that could be hurled as enemies. It was effective at sea as it could continue to burn even in contact with water. It was essential pitch or tar and oil that was then ignited. Greek fire certainly did exist and it was used as an incendiary weapon at sea. Its exact formula has been lost, but there is speculation that it contained sulphur or some petroleum compound.
Greek fire certainly did exist. Greek fire was a form of incendiary weapon, likened to napalm, that was launched towards enemy ships. The exact formula for Greek fire has been lost, through there is plenty of speculation that it contained sulphur or a petroleum compound.