A federal judge handed a key patent case to the jury, asking it to determine how much six California refiners should pay Unocal for violating a gasoline patent. The jurors' assessment could cost the defendants tens of millions of dollars and lead to higher pump prices if costs are passed on to motorists. "You must award Unocal a reasonable royalty," U.S. District Judge Kim Wardlaw instructed the 10-member jury in Los Angeles. Lawyers for both sides gave their closing arguments earlier in the day, wrapping up a phase of the 4-month-old trial. Two more phases remain: whether the defendants intentionally infringed the patent and whether it can be enforced. The defendants are Atlantic Richfield, Chevron USA, Exxon, Mobil, Shell Oil and Texaco Refining & Marketing. An Arco spokesman said the company would probably appeal the verdicts.