  A set of divisible resources becomes available over a sequence of rounds and
needs to be allocated immediately and irrevocably. Our goal is to distribute
these resources to maximize fairness and efficiency. Achieving any non-trivial
guarantees in an adversarial setting is impossible. However, we show that
normalizing the agent values, a very common assumption in fair division, allows
us to escape this impossibility. Our main result is an online algorithm for the
case of two agents that ensures the outcome is envy-free while guaranteeing
91.6% of the optimal social welfare. We also show that this is near-optimal:
there is no envy-free algorithm that guarantees more than 93.3% of the optimal
social welfare.
