  We study option prices in financial markets where the risky asset prices are
modelled by jump diffusions. It was proposed by Schweizer (1996) in a general
semimartingale setting, following earlier works by F\"ollmer and Sondermann
(1986) and Bouleau and Lamberton (1989), that the right price of such an option
is the initial wealth needed to make it possible to generate by a
self-financing portfolio a terminal wealth which is as close as possible to the
payoff F in the sense of variance. Schweizer calls this price the approximation
price and he investigates interesting general properties of this price and its
corresponding optimal portfolio.
  -However, neither of these authors compute explicitly this price in concrete
cases. This is the motivation for the current paper: We apply stochastic
control methods to compute this price in the setting of markets with assets
described by jump diffusions. Our method involves Stackelberg games and a
suitably modified stochastic maximum principle.
  We show that such an optimal initial wealth, denoted by z^, with
corresponding optimal portfolio {\pi}^ exist and are unique.
  - If the coefficients of the risky asset prices are deterministic, we show
that z^=E_{Q*}[F], for a specific equivalent martingale measure (EMM) Q*. This
shows in particular that the minimal variance price is free from arbitrage.
  -Then for the general case we apply a suitable maximum principle of optimal
stochastic control to relate the minimal variance price z^=p_{mv}(F) to the
Hamiltonian and its adjoint processes, and we show that, under some conditions,
z^=E_{Q_0}[F] for any Q_0 in a family M_0 of EMMs, described by the set of
solutions of a system of linear equations.
  -Finally, we illustrate our results by looking at specific examples.
