Chairman Ben Bernanke and The Federal Reserve will probably introduce an unprecedented second round of unconventional monetary easing today by announcing a plan to buy at least $500 billion of long-term Treasury securities over a six-month period, according to a survey of economists last week.

Twenty-nine of the 56 economists estimated the Fed will pledge to buy $500 billion or more, while another seven predicted $50 billion to $100 billion in monthly purchases without a specified total.

The remainder said the Fed would buy up to $500 billion or didn’t quantify their forecast.