Petroleum, a fossil fuel, supplies more energy to the world today than any other source. The United States is the world's leading consumer of petroleum; in 1994, Americans used 7,587,000 barrels of oil per day.
Frequently test for ammonia and nitrite (you want both to measure zero). A pH test is also handy to ensure your goldfish's water is not too alkaline or acidic. This can be purchased at any pet store. Do not modify the fish's water, however, unless it is significantly different from neutral.
It is a common practice to keep common goldfish in a small bowl but this allows waste in the water to build up to toxic levels and does not provide enough oxygen. For every small/young goldfish there should ideally be at least 10 to 20 US gallons (38 to 76 l; 8.3 to 16.7 imp gal) of water.