Little is known about the dynamic process of membrane protein folding, and few models exist to explore it. We have doubled the number of Escherichia coli outer membrane proteins (OMPs) for which folding into lipid bilayers has been systematically investigated. We cloned, expressed, and folded nine OMPs: outer membrane protein X (OmpX), OmpW, OmpA, the crcA gene product (PagP), OmpT, outer membrane phospholipase A (OmpLa), the fadl gene product (FadL), the yaet gene product (Omp85), and OmpF. These proteins share a transmembrane β-barrel motif, but vary in barrel size and primary sequence. We quantified their ability to fold into a matrix of bilayer environments by SDS-PAGE. Several trends emerged from these experiments: higher pH values, thinner bilayers, and increased bilayer curvature promote folding of all OMPs. Increasing the incubation temperature promoted folding of several OMPs but inhibited folding of others. We discovered that OMPs do not have the same ability to fold into any single bilayer environment. We show that while environmental factors are influential, OMP folding must also be modulated by intrinsic protein properties. To rationalize the differences in folding results between OMPs, we explored their kinetic profile and determined their resistance to thermal denaturation. Although these proteins share a common structural motif and have evolved to reside in the same bilayer environment in vivo, we found that these OMPs vary in their folding behavior.