Mortgage rates remained at or near record lows this week as investors — including the Federal Reserve — continued pouring money into mortgage-backed securities that fund nine out of 10 U.S. home loans.

Rates on 30-year fixed-rate mortgages averaged 3.37 percent with an average 0.7 point for the week ending Oct. 18, down from 3.39 percent last week and 4.11 percent a year ago, Freddie Mac said in releasing the results of its latest Primary Mortgage Market Survey. Rates for 30-year fixed-rate loans hit an all-time low in Freddie Mac records dating to 1971 of 3.36 percent during the week ending Oct. 4.

For 15-year fixed-rate mortgages, which are popular with homeowners refinancing, rates averaged 2.66 percent with an average 0.6 point, down from 2.7 percent last week and 3.38 percent a year ago. That’s a new low in records dating to 1991.

Rates on five-year Treasury-indexed hybrid adjustable-rate mortgage (ARM) loans averaged 2.75 percent with an average 0.6 point, up from 2.73 percent last week but down from 3.01 percent a year ago. Rates on five-year ARM loans hit a low in records dating to 2005 of 2.69 percent during the week ending July 19.

For one-year Treasury-indexed ARMs, rates averaged 2.6 percent with an average 0.4 point, up from 2.59 percent last week but down from 2.94 percent a year ago. Rates on one-year ARM loans hit an all-time low in records dating to 1984 of 2.57 percent during the week ending Oct. 4.

The $40 billion-per-month increase in government purchases of mortgage-backed securities guaranteed by Fannie Mae and Freddie Mac announced by the Federal Reserve on Sept. 13 is expected to help keep mortgage rates low for an indefinite period.

Looking back a week, a separate survey by the Mortgage Bankers Association showed demand for purchase loans at its highest level since June. The survey showed demand for purchase loans during the week ending Oct. 12 up a seasonally adjusted 1 percent compared to the week before, and up 12 percent from a year ago