LONDON (Reuters) - West African crude differentials to dated Brent came under further pressure on Friday as Nigeria's May export programme showed mostly stable volumes from the previous month. Traders said the new offers, joining the 20-odd cargoes still available from the April programme, are likely to make buyers more reluctant to pay the prices sellers want. Differentials hit eight-month highs in recent weeks on the back of strong demand via tenders from Indian refineries. There are two more such tenders, from HPCL and BPCL, pending now, and the biggest buyer of late, IOC, awarded another tender earlier this week. Nigeria's state oil company raised the April official selling price (OSP) for Qua Iboe and Bonny Light crude oil to dated Brent plus $1.25 and $1.15 per barrel respectively, reflecting the stronger market. The March price was dated Brent plus 82 cents for both grades. But traders said such prices are no longer sustainable. "The offers are too high," one said. "WAF is too expensive." Despite this, traders said sellers of Angolan crude are increasing the prices they want for May-loading cargoes because of what they view as strong demand. NIGERIA * Nigeria will increase its exports of Bonny Light crude in May to just under 213,000 bpd, the highest level so far this year, but per-day exports of Nigeria's largest stream, Qua Iboe, will fall to just under 368,000 bpd. * The full provisional programme is still emerging, but it was on track to be roughly stable from April level of just under 1.88 million bpd. * Statoil sold a cargo of Agbami for 29-30 April loading to Petrobras, but the price was not immediately available. Agbami is now sold out for April loading, but around 20 cargoes of other grades are on offer. * The closure of the Nembe Creek pipeline, which feeds Bonny Light to export terminals, was not impacting prices, traders said. ANGOLA * Discussions around the May loadings for Angolan crude began, but no sales were reported on Friday. * While the May export programme was slightly below those in April, traders said the programme is still somewhat bearish, as most expect the addition of Saturno cargoes once the force majeure on the platform supplying the grade is lifted. Operator BP said this is expected next week. * Dalia was offered at a discount of above $2 per barrel to dated Brent. * Angola expects oil production to average 1.84 million bpd this year, according a revised 2015 budget passed by parliament on Thursday. TENDERS * Indian refiner HPCL issued a tender to buy crude oil for May loading, and the option for some April loading cargoes as well. It will close next week. * A tender from fellow Indian refinery BPCL is also expected to close next week.