HOUSTON, May 24 (Reuters) - Gasoline differentials retreated 26 cents a gallon in the Portland, Oregon, spot market on Thursday, one day after peaking at $1.10 over NYMEX RBOB gasoline, traders said.

Portland gasoline finished at an 84-cent-a-gallon premium over NYMEX RBOB.

Gasoline jumped on Wednesday due to speculation BP Plc had a hit a significant snag in restarting its 225,000 barrel per day (bpd) Cherry Point, Washington, refinery.

Sources familiar with operations at the refinery said no major problem had occurred, but integrating the operations of restarting units could trigger flaring at the plant. The company was still aiming to return the refinery to full production by the end of May, the sources said.

Diesel in Portland retreated 5 cents to finish at 20 cents a gallon over NYMEX heating oil.

In the Los Angeles spot market, June CARBOB gasoline finished flat with its Wednesday price at a 25-cent premium on July NYMEX RBOB gasoline.

July CARBOB sold at 8 cents over August NYMEX RBOB in L.A.

In the San Francisco Bay market, June CARBOB was priced at even with L.A. CARBOB gasoline.

June CARB diesel in L.A. rose 1.25 cents to 7.5 cents over July NYMEX heating oil on expectations refiners would shift production to feed rising demand for gasoline, reducing diesel supply. Bay CARB diesel was flat to L.A.

EPA diesel in L.A. was 1 cent under the CARB price.

June jet fuel in Los Angeles remained at 8 cents over NYMEX heating oil.

CARBOB and CARB diesel get their name from the California Air Resources Board, which mandates their formulas. CARBOB is a gasoline meant for use with ethanol. CARB diesel is intended to reduce pollution in California's major metropolitan areas.

Outside of California's cities, ultra-low sulfur diesel as authorized by the U.S. Environmental Protection Agency is used.