OPEC’s largest African oil producer, Nigeria, is set to switch to a monthly average Dated Brent assessment when pricing its crude exports, which could ultimately make its cargoes to Europe less competitive than those of exporters sticking to a five-day average price of Brent. NNPC, the national oil company of Nigeria, plans to start using the monthly average of Dated Brent—the physical crude benchmark – for pricing its cargoes, Bloomberg reported on Tuesday, quoting a company memo it has seen. So far, Nigeria has used the five-day…