1.   But now, more of the older plants are developing problems that require unscheduled maintenance.

2.   Nevertheless, the PUC has been probing unscheduled maintenance at power plants throughout the state since last December.

3.   Refiners stepped up operations to prepare for the introduction of cleaner-burning gasoline in California, which led to unscheduled maintenance shutdowns.

4.   Supplies of refined products also tightened because of refinery interruptions and unscheduled maintenance, raising fuel prices.

5.   The company also was hampered by unscheduled maintenance at some of its refineries and a decrease in the amount of crude oil refined for heating oil.

6.   The shutdown, for unscheduled maintenance, will curb production of gasoline and other refined products.

7.   Unconfirmed reports of unscheduled maintenance at an Amoco Corp. refinery in Texas City, Texas, the largest in the U.S., also lifted gasoline prices.