We prove the existence of generalized solutions of the Monge–Kantorovich equations with fractional s-gradient constraint, 0<s<1, associated to a general, possibly degenerate, linear fractional operator of the type,
ℒsu=−Ds⋅(ADsu+bu)+d⋅Dsu+cu,
with integrable data, in the space Λs,p0(Ω), which is the completion of the set of smooth functions with compact support in a bounded domain Ω for the Lp-norm of the distributional Riesz fractional gradient Ds in ℝd (when s=1, D1=D is the classical gradient). The transport densities arise as generalized Lagrange multipliers in the dual space of L∞(ℝd) and are associated to the variational inequalities of the corresponding transport potentials under the constraint |Dsu|≤g. Their existence is shown by approximating the variational inequality through a penalization of the constraint and nonlinear regularization of the linear operator ℒsu. For this purpose, we also develop some relevant properties of the spaces Λs,p0(Ω), including the limit case p=∞ and the continuous embeddings Λs,q0(Ω)⊂Λs,p0(Ω), for 1≤p≤q≤∞. We also show the localization of the nonlocal problems (0<s<1), to the local limit problem with classical gradient constraint when s→1, for which most results are also new for a general, possibly degenerate, partial differential operator ℒ1u with coefficients only integrable and bounded gradient constraint.