The Organisation for Economic Co-operation and Development (OECD) has released a report investigating income inequalities in 30 of its 34 member states.
From 2007 to 2010, the period of the study, the growth in disparity in family income grew fastest in Spain, according to press agency EFE.
Measured using the so-called Gini co-efficient statistical analysis, the gap between the worst and best-paid families widened by 2.9%.
Slovakia came a distant second with 1.4% followed by France and Sweden with 1%.
The largest falls in average income were measured in Iceland (12%), New Zealand (8%), Greece (8%), Estonia (6%) and Mexico (6%), while Spain joined Ireland on the fringe of this group with just under 6%.
The OECD average fall in income was 2% over the three-year period.
Countries that saw their average income increase included Poland (4%) and Chile (3%).
Overall inequality was greatest in countries with high percentages of poor people including Israel (20.9%), Mexico (20.4%), Turkey (19.3%), Chile (18%), United States (17.4%), Japan (16%) and Spain (15.4 %).
The secretary general of the OECD, Ángel Gurría, commented on the data, stressing "the need to protect the most vulnerable in society, especially as governments continue the necessary mission of getting public spending under control."
He added: "Policies must be designed to promote employment and growth to ensure equality, efficiency and inclusion."
Gurría said that he considered it "essential" to reform tax systems to ensure fairness and guarantee the provision of essential benefits.
The OECD is an international economic organization of 34 countries founded in 1961 to stimulate economic progress and world trade.