UPDATE 1-Canada regulator sees moderate summer energy prices

(Adds detail. In U.S. dollars)

CALGARY, Alberta, May 28 (Reuters) - The weak global economy and brimming inventories of oil and gas will keep energy prices moderate this summer, Canada's main energy regulator said on Thursday.

In its annual summer outlook, the National Energy Board said it expects oil to average $50-$60 a barrel and natural gas to average $3.20-$4.20 per million British thermal units.

The forecasts for both oil and natural gas are much less than half last year's prices.

Oil prices have recently strengthened, trading on Thursday at more than $65 a barrel and double the lows set in December. But holding that gain will depend on strength or weakness in the economy during the summer.

"Things mainly depend on what happens to the economy," Christian Rankin, an oil market analyst with the NEB, told reporters. "If the economic picture improves we can expect prices to remain around where they are now. However if the economic situation deteriorates we may see prices averaging in the lower part of the range."

The board also predicted adequate supplies of electricity after new generation came online in several regions and transmission capacity was expanded between Ontario and Quebec and between New Brunswick and the United States in 2008. (Reporting by Jeffrey Jones and Scott Haggett; editing by Rob Wilson)