11.   The higher prices mostly reflect normal supply and demand factors, plus the increased cost of producing cleaner gasoline required by new regulations, officials say.

12.   The most important of these rulings will require automakers to build cleaner vehicles and oil companies to refine cleaner gasoline.

13.   The industry has been pleased with the cleaner gasoline rules, which will make it easier to build cleaner-burning engines.

14.   The new air pollution rules will require automakers to build cleaner vehicles and oil companies to refine cleaner gasoline.

15.   The rule requiring cleaner gasoline will make it easier for the car manufacturers to meet their new targets.

16.   To help automakers do this, the administration will also require oil companies to sell much cleaner gasoline.

17.   Unocal Corp. may have other oil refiners over a barrel if they want to sell state-mandated cleaner gasoline in California next year.

18.   All three areas are among cities that have been required to sell only a new blend of cleaner gasoline because of severe summer pollution problems.

19.   Although not generally known, motorists also are paying a premium because of a little-known patent dispute involving the blending of the cleaner gasoline.

20.   Another firm substantially increased its production of the cleaner gasoline and built up inventories.