We present dc-magnetization and ac-susceptibility measurements of the
organic superconductors kappa-(ET)(2)X with X = I-3, Cu(NCS)(2), and C
u[N(CN)(2)]Br. For all investigated materials the lower critical field
perpendicular to the highly conducting planes, B-c1(perpendicular to)
, tends to zero already 0.5 K below T-c. This might be an indication f
or fluctuation effects of single vortices expected for 2D superconduct
ors. Pinning effects lead to an apparent increase of B-cl towards lowe
r temperatures and they play an important role for the temperature and
frequency dependence of the irreversibility field B-irr determined by
ac-susceptibility.