This work reports low temperature magnetoresistance data, for various electron densities and temperatures, of a strongly coupled GaAs/Al033Ga0.67As modulation-doped double quantum well structure under an in-plane magnetic field. The in-plane magnetoresistance traces of the sample investigated show features which clearly indicate the formation of an energy gap at the crossing region between two single well dispersions. Based on an interpretation of the experimental data, an estimate of this gap is obtained, which is in good agreement with its theoretically predicted value. At high electron densities (n greater than or equal to 8.6 x 10(11) cm(-2)) clear Shubnikov-de Haas oscillations are also observed, which have been attributed to mobility enhancement of the sample with an increase of electron density in the conducting channel of the system.