Bitcoin markets are inefficient. Using ten second volume weighted average prices from February 2013 to April 2018, we show significant and increasing arbitrage spreads between global Bitcoin markets. Minimum and maximum prices per ten second interval show significant clustering. Moreover, spreads between markets follow consistent patterns: Arbitrage traders will find increased spreads during APAC trading hours, following the market entry of new exchanges as well as after bitcoin heists & hacks. Opportunities for arbitrage are stable enough for arbitrageurs to execute trades within at least one minute.