  We present a new parton distribution function analysis which includes new
data for W boson production in proton-proton collisions and lepton pair
production in proton-proton and proton-deuteron collisions. The new data
provide strong constraints on the light antiquark parton distribution functions
in the proton. We identify an interesting correlation between the $d/u$ ratio
and the $\bar{d}/\bar{u}$ ratio which leads to a modification of our previous
results for the $d/u$ ratio as the parton momentum fraction $x \rightarrow 1.$
