Previous investigations of thin film composite (TFC) hollow fiber membranes for forward osmosis (FO) have been focused on the careful design of the support layer that provides mechanical strength to a thin selective layer (typically a polyamide film). While exhibiting excellent FO performance due to a delicately tailored supporting structure, some of these membranes require complicated fabrication procedures. This has led commercial entities to criticize these academic efforts for being impractical or unattainable for conventional manufacturing procedures. These criticisms have motivated us to approach making hollow fiber FO membranes differently. In this study, we use commercial ultrafiltration hollow fiber membranes (Koch Membrane Systems) as supports for polyamide TFC membranes. These membranes were already potted into 18-in. modules before the in situ formation of the polyamide on the lumen of the fibers. Two fiber sizes were selected for comparison, and all membranes tested exhibited remarkably good FO performance (both water and solute flux) given that the supporting materials had undergone no tailoring or adjustment. The use of commercial modules also allows for volume-normalized performance metrics to be considered as a new way to define FO performance.