May be different in your area but here in Central MT there is little advantage to buying in bulk vs buying at Wal-Mart. At least for Rotella anyway. My neighbor is an over the road trucker and runs three rigs. I asked him what he buys, from who, cost etc.
He uses Shell Rotella and finds that it's basically the same, or slightly cheaper than buying bulk from a distributor. BUT....We are also 45-50 miles from any Distributors so delivery probably adds some cost.
FN in MT