Money generated by drug trafficking, prostitution, smuggling and illegal gambling contributed nearly 9 billion euros ($11.4 billion) to Spain's economy last year, according to the country's National Statistics Institute.
Their findings show that when the "shadow economy" numbers are included, the Spanish gross domestic product rises by 26.2 billion euros, totalling 1.05 trillion euros. Such activities account for nearly 1 percent of the total Spanish economy.
The figures also included revenue from a few legal activities that had previously been excluded from statistics, like military assets and research investment, said Agence France-Presse.
The GDP statistics were generated on the recommendation of the European Union's Eurostat Commission, which is attempting to estimate the true economic value of its member states, which requires statistics on their illicit shadow economy activities.
According to AFP, Eurostat "ordered countries to provide data on lucrative activities such as prostitution and drug-dealing on the grounds that they were a trade carried out willingly by participants."
To account for Spanish drug sales, the institute examined official numbers regarding the quantity of drugs seized by law enforcement. To determine how much revenue sex work had generated, it counted the number of known prostitutes and, "in consultation with sex clubs, calculated how much they earned," stated the Washington Post.
Yet some, like the Spanish tax-collectors' union Gestha, told AFP that the method of estimating income from illegal activities was far from accurate, describing it as "a form of window-dressing that will enable the government to present better figures for the national deficit and debt."
Gestha estimated that Spain's shadow economy accounted for nearly a quarter of its GDP in 2012.
While European law requires countries to account for illicit activities, many do not comply due to the difficult nature of determining accurate figures.
A few countries reportedly refused to comply with Eurostat's request. France and Sweden both said they will not provide data on prostitution, since prostitution may occur unwillingly.
Italy released its revised GDP figures last week, which shows a growth of 3.8 percent from previous estimates.
