I agree with indolent that it is probably gravity fed LME. However, I disagree with indolent in the statement that the remaining LME will have contact with O2. I think the LME near the tap will have contact with O2; seeing as LME is rather viscous, I doubt the rest of the drum will have contact with O2 past the spigot. The drum itself will not allow UV penetration (to a point). Ask your LHBS if they brew with the same LME from that same drum; if not, question as to why not and why you (the customer) should.