LONDON (Reuters) -Oil prices edged up on Thursday after Saudi Arabia's state oil company raised its March crude prices sharply, but the gains barely dented the previous day's slide in benchmark Brent crude. Brent crude futures rose 44 cents, or 0.6%, to $75.05 a barrel by 1355 GMT. Oil prices had plunged by more than 2% on Wednesday as a large build in U.S. crude and gasoline stockpiles signalled weaker demand while investors also weighed up the implications of a new round of U.S.-China trade tariffs, including duties on energy products.