U.S. equities markets reacted positively to news from Brussels that European Union leaders agreed Friday on a tighter fiscal union, a move meant to preserve the euro as a viable currency.

Stock in the largest American banks were particularly bullish on the developments, trading up in heavy volume during pre-market action in the New York Stock Exchange. Shares of Citigroup (NYSE:C), Bank of America (NYSE:BAC) and Goldman Sachs (NYSE:GS) rose more than 2 percent in very early pre-market trading. Morgan Stanley (NYSE:MS), whose operations are generally considered to be more sensitive to developments out of Europe than its large bank peers in the U.S., jumped more than 3 percent.

The rally extended into early regular-session trading in New York, with those three bank stocks among the five most-heavily traded issues in the namesake stock exchange during early-morning dealing. Bank of America was particularly heavily traded, with volume exceeding 55.3 million shares changing hands by 10:30 a.m. New York time. That amount of trading was more than double the volume experienced by the next most active issue, AMR Corp., which experienced volume of 26.5 million as shareholders in that bankrupt company scrambled to position themselves prior to the firm's upcoming delisting.

Shares continued to be widely up in mid-morning trading. The KBW Bank Index, a benchmark index of the largest U.S. banks, was up 2.13 percent to 38.90. Morgan Stanley and Citigroup led the large banks up, gaining 3.72 and 3.91 percent, respectively. Bank of America, Wells Fargo (NYSE:WFC), JPMorgan Chase (NYSE:JPM) and Goldman Sachs, were all trading up more than 2 percent.