Most crowds expect Jim Macias to be on the defensive these days. Oil prices are down some 33% and the theme of North American International Auto Show in Detroit earlier this month was making cars that are friendlier to the environment.

At Shell, where he is a manager in the company’s Fuel Technology Group, Mr. Macias is in charge of investigating which fuels will replace gasoline and developing ways to make them cheaper.

But so far, there’s nothing in the pipeline that he said will transform Shell or dramatically change the way the world’s vehicles are powered.

“Fossil fuels will dominate the transportation world for the next 100 years,” Mr. Macias told the International Motor Press Association yesterday. “Shell’s an open-minded company, but as long as the demand is there, we’re going to refine oil and gas until anything else becomes more cost effective.”

Mr. Macias said the worldwide infrastructure designed to explore, extract, and refine oil is so vast and established that virtually no economic force could justify its replacement. Oil companies like Shell think a more realistic outcome is that more efficient fossil fuels will take up more of the functions at those plants.

To be sure, the energy industry must follow the automotive world. And so far, gas hybrid vehicles — and diesels in Europe — don’t suggest any radical departure from traditional oil and gas.

If Shell has a “green” side, it’s the work Mr. Macias and his team is doing to promote bio-fuels that are made from bio-waste. “Instead of making ethanol from cornmeal and soybeans, which is more expensive, we’re looking at how to derive gas from husks and woodchips, stuff that’s not going to be used by anyone,” he said.

Companies aiming to break down large “woody” molecules from the waste products of plants into sugars — which energy firms can distill into gasoline — are exciting investors. In North America, Shell is partnering with Iogen Corporation, a Canada-based company that has helped it make ethanol from straw.

In Europe, the developments are more exciting from the standpoint of diesel, a largely underappreciated fuel in America, Mr. Macias said. Shell is working with Choren Industries there to turn the same types of pulp by-products into diesel hybrids.

“Let’s face it: Bio-fuels are the only viable short-term option we have in a world dominated by fossil fuels,” Mr. Macias said. The socalled GTL market (gas-to-liquid) is another attractive plan preached by green advocates, but, like electricity before it, GTL is extremely expensive. Plus, Mr. Macias said, drivers have yet to embrace the idea of riding around with a loaded hydrogen tank on board.

In 1950, there were 80 million vehicles that produced 70 million tons of carbon dioxide. By 2050, there will be two billion vehicles. The greenhouse gas emission question is what oil companies are trying to answer.

Part of the answer comes in Shell’s handbook, “Fueling Mobility,” which states that 8% of the world’s population will live in urban areas by 2050. Shell’s suggestion: Consider walking or riding your bike.