Using detailed information from a large sample of investment banks we test the determinants of IPO allocations. This research draws on data gathered by the UK Financial Conduct Authority, and covers 220 IPOs managed from the UK raising around $160bn. Detailed information on book-building is combined with data on revenues generated (from trading and other activities) by investment banks’ buy-side clients. We find evidence that informative bids are rewarded. However, we also find strong evidence that most, but not all, of the major investment banks favor the buy-side clients that produce the most revenue.