(Adds maintenance, Forties price.) By Sherry Su Of DOW JONES NEWSWIRES LONDON (Dow Jones)--One standard 600,000-barrel cargo of North Sea Forties crude has been dropped from August loading program due to low production, further tightening the physical market, traders said Wednesday. The dropped cargo is the one with parcel number F0815 for Aug. 23-25 loading, and its equity holder is Royal Dutch Shell PLC (RDSA), they said. The cargo was dropped due to "lower than expected production," said a trader. This came after at least eight cargoes for August loading were deferred by one-to-three days amid planned maintenance and production hiccups. BP PLC (BP) will shut its Unity Riser platform, a key part of Forties Pipeline System in the North Sea, on Aug. 1 for three or four days of maintenance. Some technical problems occurred recently on the FPS, which BP operates. Two weeks ago, a valve failure prompted Nexen Inc. (NXY) to shut its Scott platform in the North Sea. Also, production at Nexen's 200,000-barrel-a-day Buzzard field, the largest in Forties system, wasn't stable earlier this month. Tight supply of Forties crude has pushed the differential of Forties crude to a two-year high. Tuesday, BP sold one 600,000-barrel cargo for Aug. 11-13 loading to Vitol Holding at a premium of $1.05 over Dated Brent, the highest since March 2008. Forties usually sets benchmark Dated Brent, which is used to price nearly 60% of global crude trades. Dated Brent has been pegged at a premium to front-month Brent futures on London's ICE futures exchange for more than two weeks, mainly because of the tightness of Forties supply. -By Sherry Su, Dow Jones Newswires; +44(0)20-7842-9329; sherry.su@dowjones.com (END) Dow Jones Newswires July 28, 2010 11:38 ET (15:38 GMT)