The MERVAL Index (MERcado de VALores, literally Stock Market) is the most important index of the Buenos Aires Stock Exchange. It is a price-weighted index, calculated as the market value of a portfolio of stocks selected based on their market share, number of transactions and quotation price. The base of MERVAL is set at 30 June 1986 = 0.01 Argentine pesos.
The corporations and weighted prices that compose MERVAL are updated every three months, based on their market share during the previous period.
As of May 2017 the companies in it are Aluar (aluminium smelter), BBVA Banco Francés, Banco Macro, Sociedad Comercial del Plata (holding), Edenor (electricity), Grupo Financeiro Galícia (financial), Pampa Energía, Petrobras Argentina, Ternium(=Siderar)(steel), Telecom Argentina(telco), Tenaris (steel pipes), YPF (oil and gas). 
The following is a table showing the annual maximum, minimum and average values of MERVAL between 1996 and 2005. During that period, the index hit its minimum value in 2001, some time before the explosion of the economic crisis, but recovered in an accelerated fashion after that.