The field dependence of the resistivity and the critical current density, J(c)(B), of MgB2 doped with 10 wt% wet and dry succinic acid have been investigated by magnetic measurements. The dry succinic acid significantly enhanced the upper critical field, the irreversibility field, and the J(c)(B) compared to the wet succinic acid doped MgB2 and the pure MgB2. The field dependence of J(c)(B) was analyzed within the collective pinning model. The observed temperature dependence of the crossover field, B-sb(T), from the single vortex to the small vortex bundle pinning regime shows that flux pinning arising from variation in the critical temperature, delta T-c,, is the dominant mechanism for the wet sample over the whole studied temperature range, while there is a competition between delta T-c pinning and the pinning from variation in the mean free path, delta l, for the dry sample. (C) 2013 Elsevier Ltd. All rights reserved.