We consider the problem of finding two free export/import sets E + and E − that minimize the total cost of some export/import transportation problem (with export/import taxes g ±), between two densities f + and f − , plus penalization terms on E + and E −. First, we prove existence of such optimal sets under some assumptions on f ± and g ±. Then, we study some properties of these sets such as convexity and regularity. In particular, we show that the optimal free export (resp. import) region E + (resp. E −) has boundary of class C 2 as soon as f + (resp. f −) is continuous and ∂E + (resp. ∂E −) is C 2,1 provided that f + (resp. f −) is Lipschitz. This is a ``preproof'' accepted article for Canadian Mathematical Bulletin This version may be subject to change during the production process.