BOK Financial Corp. (BOKF) in Tulsa, Okla., fell short of Wall Street's quarterly earnings estimates due to the mortgage slowdown, margin compression and higher costs for bad loans.

The $27.3 billion-asset company earned $75.7 million in the third quarter, down 13% from the same period of 2012, it reported Wednesday. Earnings per share of $1.10 were 5 cents below the average estimate of analysts polled by Bloomberg.

Net interest revenue dropped by 5%, to $166.4 million, the net interest margin tightened by 32 basis points, to 2.80%. The bank's made an $8.5 million provision for loan losses after taking no provision in the year-prior period.

"This quarter proved to be challenging as uncertainty over government policies continued to drive higher long-term interest rates," said Chief Executive Stan Lybarger in a news release.

BOK saw a 19% drop in its noninterest revenue, mostly due to a 53% decline in mortgage fees, to $23.5 million. The bank's mortgage revenue was hurt both by lower sales margins and a decline in production. Earlier this month, BOK launched an online mortgage sales channel that allows it to offer loans nationwide.

The bank's revenue from brokerage and trading, card transactions and trusts rose, partially making up for the mortgage slowdown. BOK agreed to buy GTRUST Financial, an asset manager based in Topeka, Kan., earlier this month and it expects the deal boost trust income in future quarters.

BOK's overhead costs fell 5%, to $210.6 million, largely due to lower mortgage banking costs and lower charges related to mortgage servicing rights.

In June, BOK announced that Steven Bradshaw would succeed Lybarger as CEO at the end of the year.

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