The OLGA Verification and Improvement Project for Three-Phase Flow is a joint industrial project sponsored by 11 oil companies to improve the flow models in OLGA and verify the improved code against field data. To improve the stratified flow model, correlations for wall shear and entrainment were improved based on published experimental data as well as unique in-house data. For slug flow, the translational velocity and slug body pressure drop have been improved using models from literature. The improved OLGA code has been compared to the AGA data bank for wet gas pipelines and to data from Prudhoe Bay. The comparisons show that systematic prediction errors are greatly reduced.