mstram,
Can't answer re B767, but on the Brits revenge, the BAe146, in standard fit, there are 3 fuel tanks. One in each wing and a centre tank, basically in the fuselage roof.
The capacities in round figures are: 3650 kg per wing and 2000 kg in the centre tank.
The AFM limits fuel asymmetry between wings to a maximum of 680 kg (1500 imperial lb). There is no reason given that I am aware of, and assume the reason could vary between aileron/roll spoiler ability to keep wings level (which I doubt), to bending moments at the wing root, to something else I've never considered.