Oil prices erased earlier gains on Tuesday falling more than USD 2 a barrel after investors booked profits from the previous day`s rally and on expectation of slowdown global energy demand.Light, sweet crude for November Delivery lost USD 2.56 to settle at USD 78.63 a barrel on the New York Mercantile Exchange (NYMEX). In London, November Brent crude dropped USD 2.93 to close at USD 74.53 a barrel on the ICE Futures exchange.In other NYMEX trading, heating oil futures declined 8.13 cents to