BUENOS AIRES, Feb 19 (Reuters) - Argentina's stock, currency and bond market trends on Thursday:
* The benchmark MerVal stocks index .MERV gained 1.02 percent to 1,065.67 points, rebounding after three sessions of losses as energy shares got a boost from a sharp rise in U.S. crude oil futures.
* The gains came despite an announcement by equity index provider MSCI Barra MXB.N that it will reclassify Argentina as a frontier market from an emerging market, due to its restrictions on capital flows.
* The Buenos Aires-listed shares of Brazilian state energy firm Petrobras APBR.BA, which carries a 12 percent weighting on the MerVal, rebounded 4.7 percent to 50.60 pesos.
* On the broad market, volume was weak at $8.8 million. Among active issues, 20 advanced, 30 declined and 12 ended unchanged.
* Government bonds traded over the counter in Buenos Aires rose 0.4 percent on average as investors took advantage of recent declines, which had been spurred by risk aversion.
* The peso-denominated 2038 Par bond ARPARP=RASL jumped 2.1 percent, according to the ask price.
* In formal exchange between banks, where the central bank regularly intervenes to avoid abrupt movements, the peso weakened 0.64 percent to 3.5325/3.535 per dollar ARS=RASL.
* In informal trade between foreign exchange houses, as measured by Reuters, the peso currency slumped 1.25 percent to 3.605/3.61 ARSB=, its lowest level since December 2002.