* Nigerian Qua valued at dated plus $2.25-$2.50
* IOC, Petral issue tenders for May-June
GENEVA, April 5 (Reuters) - Asian buyers issued fresh tenders for May and June, raising prospects that West African differentials might soon reach a floor after falling steadily this week.
Asian demand for West African cargoes has fallen from record levels in the first quarter of this year partly due to rising supplies of similar grades such as Libyan.
But traded levels for late Wednesday and Thursday were still lower and traders said that around 20 cargoes of Nigerian grades were still available.
"Levels are still coming off," said a West African crude oil trader.
* Qua Iboe: Exxon was heard to have sold a cargo for mid-May loading to U.S. refiner Sun. U.S. demand for Nigerian cargoes from the May programme has generally been depressed.
* Traders assessed this grade little changed at dated plus $2.25-$2.50 a barrel.
* Bonny: Two cargoes from the May programme traded late on Wednesday or Thursday but levels could not be confirmed.
* Nemba: traders said that at least two cargoes for May loading were still unsold.
* Petral, the trading arm of Indonesia's Pertamina, issued a tender for crude oil for delivery between 18-25 June, traders said.
* The tender will close on Monday April 9. The volume sought is one cargo of either 650,000 barrels or 950,000 barrels and accepted grades include Angolan, Libyan and Brazilian grades.
* India's IOC also issued a tender for light, sweet crude for loading in the second half of May or early June, a tender document showed.
* Offers for the two-part tender are valid until April 12.
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here (Reporting by Emma Farge; Editing by Anthony Barker)