Private bondholders must decide whether to swap their Greek debt at a loss by 2000 GMT on Thursday. "Tonight at midnight, a procedure of historic character reaches completion. An operation of unprecedented size and complexity to drastically cut Greek state debt," Finance Minister Evangelos Venizelos told parliament. Officials would need two hours after the deadline to determine the level of participation, Greek news reports said. The swap is designed to erase more than 100 billion euros ($132 billion) of the country's debt, which totals more than 350 billion euros. European stock markets posted strong gains in midday deals on Thursday following rises across Asia and in the United States on optimism that Greece's debt swap would be successful, and owing to strong US jobs data. Greece's own stock exchange showed a gain of 1.73 percent in early afternoon trade. Thursday's deadline for a decision concerned all bonds, a finance ministry source said. Creditors holding more than half of the total had already agreed to participate in what is essentially a controlled default aimed at calming a crisis that concerns the entire eurozone. Greek media on Thursday put the participation higher, at more than 70 percent. The Greek government would like to have acceptances for 90 percent of private creditor debt, and has said it will not go through with the deal unless participation reaches at least 75 percent. The Greek government will make an announcement on the swap on Friday, a finance ministry source said, declining to comment on the takeup rate. "An announcement will be made at 0600 GMT on Friday on the official government site for the exchange (www.greekbonds.gr)," the official said, although a late-night statement by Finance Minister Evangelos Venizelos "could not be excluded." The Eurogroup of eurozone finance ministers was to review the outcome at a teleconference on Friday, and meet on Monday in Brussels, Finance Minister Evangelos Venizelos said Wednesday. A half-dozen Greek pension funds with holdings of about 3.5 billion euros have declined to participate, the finance ministry source said, but could be forced to do so under so-called collective action clauses recently included in Greek law. Under this legislation, the exchange becomes binding for bonds governed by Greek law if at least half of all bondholders make a decision and at least two thirds of them approve the proposed amendments. Greece and the Institute of International Finance (IIF), which represents leading global banks, have painted a dark picture of what the possible consequences might be if the country was forced into a disorderly default on March 20, when it is due to reimburse 14.4 billion euros in debt. An IIF report warned that if the debt swap deal failed, it could do serious damage to the eurozone and even the global economy. Published on Monday, the report put the price tag of a Greek default at one trillion euros. The bond swap essential to unlock a 130-billion-euro bailout from Greece's eurozone partners, with Athens having already adopted a package of painful austerity cuts. The debt writedown is the biggest ever attempted, overshadowing Argentina's $82-billion default in 2002, the equivalent of 73 billion euros. Despite the generally positive atmosphere underscored late on Wednesday, surprises were possible up to the last minute if many Greek bondholders declined to participate. German Finance Minister Wolfgang Schaeuble warned that Greece would face a "disaster" if its financial system cannot be saved.