Since April 172 million gallons, or 4 million barrels, of crude petroleum has discharged into the Gulf of Mexico, causing unheard-of damage to the gulf and coastal environments in the largest oil spill ever recorded.

From this refineries could produce 85 million gallons of gasoline, enough to drive 1.6 billion miles, nearly seven miles per vehicle in the United States, not counting industrial and farm equipment.

For most of us the word "oil" brings to mind a liquid lubricant like motor oil. Few of us have encountered crude oil, more correctly called petroleum, which comes out of the ground in many different colors, textures and viscosities.

It became petroleum only after the sludgy remains of tiny, brainless plants were cooked to several hundred degrees as a result of slow burial under thousands of feet of sediment over millions of years. When it reached maturity it seeped upward through permeable rock until an impermeable cap trapped it.

Petroleum is the general term for the chemical remains of fossilized sunlight that contains hundreds of different hydrocarbon molecules of various shapes, sizes and molecular weights in a single sample of crude. Different varieties of crude contain a unique collection of molecular types.

Of all fractions of petroleum, the greatest demand is for gasoline, which is naturally about 40 percent of the crude but can be made greater than 50 percent by converting other molecules to gasoline. Industrial procedures break down large molecules, change the molecular structures of low- quality gasoline molecules or form longer molecules by chemically combining smaller ones.

About 10 percent of the crude is used to make a variety of compounds that go into the manufacture of plastics, paints, pesticides, pharmaceuticals, cosmetics, textiles and nearly everything else that is man-made. There is a quantum of petroleum in 95 percent of the goods in shops.

Even products that would seem to have no connection to petroleum have their quantum. Vegetables in the supermarket encased in plastic are grown with fertilizer that required oil-burning energy to produce, farmed with oil-burning machinery, refrigerated in oil-burning coolers, transported by oil-burning trucks over asphalt highways.

The average American uses about 3 gallons of petroleum in various forms every day for a staggering total of 1 billion gallons per day. All of the petroleum that has gushed into the gulf waters since the blowout would fuel Americans’ needs for about 2 1/2 hours.

This is not to imply that the introduction of that much petroleum into the ecosystem is not serious. It is documentable on the sea surface and on the flora and fauna of the surface and shoreline. We do not know the extent of the damage to the sea floor ecosystem of the gulf.

The global use of petroleum is approaching 90 million barrels per day. How characteristically human that we should be concerned about the environmental effects of a spill of 4 million barrels while belittling the larger effects of the byproducts of 20 times that amount every day on the global ecosystem.