Sulfur speeds oil formation in lab.

Once, a popular rags-to-riches scenario involved stumbling upon an unknown oil deposit under the backyard--a discovery valuable enough to turn an ordinary citizen into an oil baron. In reality, petroleum companies spend a lot of money and effort trying to predict before they drill whether a spot will yield a gusher or a dry well.

Oil deposits build up from layers of organic matter that decomposes--over enough time and at sufficiently high temperatures--into a complicated mix of hydrocarbons. Oil companies use mathematical models to calculate whether enough time has passed for a particular set of geologic conditions to yield a pot of black gold.

The roil of chemical reactions that turns dead plants and animals into oil can thwart even the best prognosticators. One ingredient, a reactive form of sulfur, appears to be critical in determining how quickly oil forms, says Michael D, Lewan of the U.S. Geological Survey in Denver.

In their painstaking search for hidden deposits, petroleum companies occasionally find oil in surprising places. These unexpected deposits, which tend to be rich in sulfur, prompted Lewan to propose in 1985 that sulfur-containing organic material turns into oil more readily than standard models predict.

He suggested that decomposition might go faster simply because carbon-sulfur bonds split more easily than carbon-carbon bonds, but the explanation didn't account for the diversity of components in petroleum, he says. He then theorized that sulfur radicals could accelerate breakdown.

Lewan's recent experiments show that a reactive form of sulfur speeds up oil formation by stimulating the breakdown of hydrocarbon molecules. He baked a hydrocarbon--chosen to mimic a partially decomposed precursor, to oil--in a closed capsule at 350 [degrees] C for 3 days, with and without a sulfur compound. The compound, known to create radicals, increased hydrocarbon breakdown by more than 20 percent, Lewan reports in the Jan. 8 Nature.

The presence of these sulfur radicals could help explain the composition of petroleum and offer a new way of estimating the time it takes for oil deposits to form in the earth, he says.

Alan Burnham of the Lawrence Livermore (Calif.) National Laboratory disagrees with Lewan's analysis, saying that the results don't reveal the real-world relationship between time, temperature, and sulfur content. "Everyone agrees that sulfur lowers the temperature of oil formation," he says, "but the question is, by how much?"