We compute by computer simulations the solvation force of a system of linear and branched alkanes confined in a slab geometry. The solvation force for linear decane oscillates with distance with a periodicity close to the width of the molecules. The branched alkanes, 2-methylundecane and 2-methylheptane, show a similar oscillatory behaviour, however the oscillations are decreased with a factor of about three and show a long-range attractive force. In addition, we show that the critical temperature of the liquid-vapour coexistence of n-pentane shifts to lower temperatures upon confining.