Mark D Your premise assumes that BA (And any other airline) knows in advance what the Oil Prices are to be. if they could do that, they could (And should) get right out of the Airline business and make their fortune speculating on the stock exchange and
guarantee a profit.!!
If one carrier puts their surcharge up more or sooner than another, it ignores the fact that thier cost base is hugely different.
Example.... BA and QF on their common rute stations (eg: Singapore, Sydney, London, Frankfurt etc etc etc) pool their fuel buying power so that their fuel costs are lower than the carrier who operates once, twice three times etc per week. Simple premise....the customer with the highest volume purchases gets the lowest price. It's the Law of supply and demand.
