We experimentally examine pre-trade transparency in fragmented limit order markets. Allowing traders to hide their orders encourages limit order usage. This improves measures of liquidity by increasing depth and narrowing spreads. However, because some of this depth is not displayed, market fragmentation may limit traders’ ability to capitalize on the improved liquidity. This happens when traders execute against orders at worse prices than orders in another market, often referred to as “trade-throughs.” In our laboratory setting, increased trade-throughs in a dark market impose costs of similar magnitude to the benefits of increases in depth leaving effective liquidity unchanged.