Price clustering in financial markets is pervasive. Using transaction-level data from the world's largest financial market, this study is the first to examine price clustering behavior in the foreign exchange swap market. In addition to existing hypotheses, we investigate new determinants of price clustering including the expected return, contract liquidity, and trader's identity. The results support both negotiation and price resolution hypotheses. We find a positive effect from the level of expected return on price clustering. Markets with greater liquidity experience reduced clustering. Transactions involving domestic banks have less clustering suggesting an information advantage over foreign banks.