The Mexican peso plunged again.

Mexico’s currency has fallen to its lowest level since November, and private analysts blame investors’ fears over the effect that lower world oil prices will have on the country’s troubled economy. Private exchange houses in Mexico City on Friday offered 500 pesos for each U.S. dollar on the free market and demanded 515 pesos from those wanting to buy. Late in the day, they lowered the rates to 485 and 500 pesos, respectively. Along the U.S.-Mexico border, U.S. banks were quoting rates of 470 pesos for each dollar bought and 491 for each sold. The free-market rate for the peso is used in tourism and for most border and private transactions.