Japanese retail foreign-exchange investors increased dollar-yen sell positions 17.7% day-over-day between September 10 and 11, according to Gaitame.com's Gaika Next Neo trading service. The shift reflects uncertainty ahead of the U.S. Consumer Price Index (CPI) release on September 11, with high oil prices supporting dollar-buying and yen-selling while expectations for additional Bank of Japan rate hikes provide a countervailing yen-supporting factor. Dollar-yen rose to 154.666 yen after oil prices surged on reports involving Yemen's Iran-backed Houthi forces and expectations of a sharp Saudi Arabian production decline, then fell to around 153.85 yen after a hawkishly interpreted European Central Bank (ECB) meeting. The pair later rebounded to 154.610 yen in Asian trading before adjustment selling pushed it to around 153.05 yen. Trading volume remained 24% above its 20-day average but fell 15.0% from the previous day. Buy positions represented 61% of open positions, although sell positions rose 5.2%. Dollar-yen accounted for 87.0% of currency-pair trading, while Mexican peso-yen, GBP/JPY and New Zealand dollar-yen gained share; Turkish lira-yen fell to sixth place. EUR/USD buy positions increased 3.3% after the ECB meeting. U.S. August Producer Price Index (PPI) inflation accelerated to 5.4% year over year, while the U.S. Treasury's long-term bond buyback program totaled $5.19 billion, below the expected $6 billion, supporting dollar demand. Attention now centers on U.S. CPI and how higher import prices from oil affect Bank of Japan policy management.