Experiments have been conducted to study the turbulent heat transfer and friction for fully developed flow of air in a square channel in which two opposite walls are roughened with 90 full ribs, parallel and crossed full ribs with angles-of-attack () of 60 and 45, 90 discrete ribs, and parallel and crossed discrete ribs with = 60, 45, and 30. The discrete ribs are staggered in alternate rows of three and two ribs. Results are obtained for a rib height-to-channel hydraulic diameter ratio of 0.0625, a rib pitch-to-height ratio of 10, and Reynolds numbers between 10,000 and 80,000. Parallel angled discrete ribs are superior to 90 discrete ribs and parallel angled full ribs, and are recommended for internal cooling passages in gas turbine airfoils. For = 60 and 45, parallel discrete ribs have higher ribbed wall heat transfer, lower smooth wall heat transfer, and lower channel pressure drop than parallel full ribs. Parallel 60 discrete ribs have the highest ribbed wall heat transfer and parallel 30 discrete ribs cause the lowest pressure drop. The heat transfer and pressure drops in crossed angled full and discrete rib cases are all lower than those in the corresponding 90 and parallel angled rib cases. Crossed arrays of angled ribs have poor thermal performance and are not recommended.