  Markets with multiple divisible goods have been studied widely from the
perspective of revenue and welfare. In general, it is well known that envy-free
revenue-maximal outcomes can result in lower welfare than competitive
equilibrium outcomes. We study a market in which buyers have quasilinear
utilities with linear substitutes valuations and budget constraints, and the
seller must find prices and an envy-free allocation that maximise revenue or
welfare. Our setup mirrors markets such as ad auctions and auctions for the
exchange of financial assets. We prove that the unique competitive equilibrium
prices are also envy-free revenue-maximal. This coincidence of maximal revenue
and welfare is surprising and breaks down even when buyers have
piecewise-linear valuations. We present a novel characterisation of the set of
"feasible" prices at which demand does not exceed supply, show that this set
has an elementwise minimal price vector, and demonstrate that these prices
maximise revenue and welfare. The proof also implies an algorithm for finding
this unique price vector.
