21.   Prices were boosted by strong demand during the summer driving season and by a series of refinery problems.

22.   Refinery problems have contributed to the surge in prices on the West Coast.

23.   Refinery problems in California have sent prices creeping upward as supply tightened in the past week.

24.   Refinery problems that helped send gasoline prices to six-month highs earlier this summer now are mostly resolved.

25.   Second, West Coast refinery problems have plagued the industry in recent months and reduced supply.

26.   The refinery problem is one of many that threatens gasoline supplies at a time of peak demand.

27.   The refinery problems around the Atlantic Basin coincide with a recent shortage of methyl tertiary butyl ether, an important gasoline additive.

28.   The Shell refinery problem has pushed up gasoline prices in Europe, he said.

29.   The refinery problem is one of many that threaten gasoline supplies at a time of peak demand.

30.   Then that gasoline was going to be supported by the refinery problems.