  Despite intense studies the exact nature of the order parameter in
superconducting Sr2RuO4 remains unresolved. We have used small-angle neutron
scattering to study the vortex lattice in Sr2RuO4 with the field applied close
to the basal plane, taking advantage of the transverse magnetization. We
measured the intrinsic superconducting anisotropy between the c axis and the
Ru-O basal plane (~60), which greatly exceeds the upper critical field
anisotropy (~20). Our result imposes significant constraints on possible models
of triplet pairing in Sr2RuO4 and raises questions concerning the direction of
the zero spin projection axis.
