31.   But it also is formed when natural gas, gasoline, diesel fuel and other fossil fuels are burned and the vapors react with sunlight.

32.   But making diesel engines as clean as gasoline engines is particularly difficult because current regulations, particularly in California, allow diesel fuel to be much dirtier than gasoline.

33.   But scientists say that diesel fuel can also be toxic when spilled, and are calling at the very least for tighter controls on fuel supply vessels.

34.   But the hulking machines run on diesel fuel, canceling out one environmental gain with a plume of sooty exhaust.

35.   But that is not the case for the thousands of trucks delivering gasoline or diesel fuel or jet fuel or less lethal substances, industry officials said.

36.   But those recordings as well as a videotape showing several defendants mixing diesel fuel and fertilizer in a Queens garage, provided strong evidence of the bombing plot.

37.   But two days ago the Northern Alliance poured diesel fuel into the underground rooms and set fire to it.

38.   But the study also pointed out some problems with diesel fuel, Ropeik said.

39.   But they can be thwarted by many factors like poor maintenance or a shortage of diesel fuel.

40.   But without the dye, collecting the proper tax on diesel fuel would be problematic.