SINGAPORE (Reuters) - Pakistan State Oil (PSO) bought a total of 160,000 tonnes of gasoline for fourth quarter delivery at a time when ample supplies rule in its favour, traders said on Thursday. The refiner bought four 87-octane cargoes, each at 40,000 tonnes, at premiums of $38.41-$45.41 a tonne to Middle East naphtha quotes on a cost-and-freight (C&F) basis. These premiums were down by around 30-35 percent from a previous purchase for up to 210,000 tonnes for September-October delivery. Gasoline usually does not do that well after the U.S. summer driving season ends, as its demand for Asian barrels fall after that, said a Singapore-based trader. The weak sector was reflected in crack spreads, where Thursdays values hit a new low for this year at $1.80 a barrel. PSO will get its fourth quarter supplies from Total and Trafigura. Total will supply a parcel for October arrival at Karachi at a premium of $42.90 a tonne. Trafigura will supply the remaining three cargoes, one for October delivery at a premium of $45.41 a tonne, while November and December parcels will each be priced at a premium of $38.41 a tonne.