Solutions to the R_b, R_c, and α_s puzzles by vector fermions

We propose two minimal extensions of the standard model, both of which can accommodate the recent puzzling observations about the excess in R_b and the deficit in R_c. The discrepancy in the low energy and high energy determinations of α_s can be resolved in the second model. Each model requires three additional heavy vectorial fermions. The current phenomenological constraints and the new potential phenomena are also discussed.