The Mexican peso had another bad day on Thursday, depreciating to 18.37 to the US dollar before strengthening slightly.

The last time the peso was weaker than that level against the greenback was in late March.

At 2:30 p.m. Mexico City time, the peso had regained some ground to trade at 18.29 to the dollar, according to Bloomberg. Based on that exchange rate, the peso depreciated 1.9% on Thursday, after trading at 17.95 to the dollar at the close of markets on Wednesday.

The USD:MXN was 17.42 at the close of markets last Friday, meaning that the peso has depreciated about 5% so far this week.

The newspaper El Financiero reported that the peso weakened on Thursday due to a decline in oil prices and expectations that the United States Federal Reserve could raise interest rates early next month.

The currency also dipped on Tuesday after the publication of U.S. data that showed there were more job openings than expected in August. That raised expectations that the Fed could increase rates again this year.

At 11.25%, the Bank of Mexico’s benchmark interest is well above that the Fed’s 5.25-5.5% target range. Analysts cite the broad gap between the two rates as one factor that has helped the peso appreciate this year after it started the year at about 19.5 to the greenback.

With reports from El Financiero