Informal networks are often emphasized as facilitating knowledge transfer. However, we find that formal networks also contribute significantly to knowledge transfer, and in fact contribute more than informal networks. This is particularly the case when knowledge is transferred between units. Additional analysis shows a synergetic effect between formal and informal ties, which suggests that knowledge transfer effects that in previous studies were attributed to informal networks only, may in fact be caused by the combination of both formal and informal networks. We conclude that there is more than one path to transfer knowledge effectively.