Abstract We report the effects of a distribution of T c 's on the measurements of the anisotropic superconducting thermodynamic parameters from reversible dc magnetization. We first present new results on a fully-oxygenated YBa 2Cu 3O 7 crystal with H ⊥ c and find that dH c / dT=−211 Oe/K and κ = 280. Then, for H ‖ c, we examine the effects of introducing oxygen defects through an annealing process and find that the same analysis produces dH c / dT = −86 Oe/K and κ∼20. Attempts to use the distribution of T c 's to extract intrinsic, bulk parameters from this broad-transition crystal are discussed. Such analysis, here applied to an ideal system, will be especially relevant for the randomly-doped cuprates.