Education is the most popular cause among the top philanthropists in the world, according to a study by wealth consultancy Wealth-X and Business Insider. Eighteen out of world's top 20 top philanthropists focused on educational initiatives in their giving, whether operating through their foundations or direct donations, says the study.Among major initiatives, the study notes that Michael Bloomberg, founder and CEO of Bloomberg, has donated over $1 billion to his alma mater John Hopkins University alone.According to the study, Microsoft co-founder Bill Gates was No. 1 on the list of top philanthropists, with $27 billion in lifetime donations as of October 2015. Wipro chairman Azim Premji was ranked 4th among the world's 20 most generous people.The top 20 philanthropists have given a total of $106.8 billion to a variety of philanthropic causes, ranging from environment and human rights to sports and entrepreneurship, says the study.After education, healthcare initiatives were the second most prominent cause among the top philanthropists. In 2014, Bill Gates announced that he would donate over $500 million through his Bill & Melinda Gates Foundation to fight malaria and other infectious diseases in the developing world.The study listed social and humanitarian services, community development, and arts and culture causes supported by the world's biggest individual donors.Here are the 20 most generous people in the world, according to the study:1) Bill Gates (lifetime donations: $27 billion)2) Warren Buffett, CEO of Berkshire Hathaway ($21.5 billion)3) George Soros, founder of Soros Fund Management ($8 billion)4) Azim Premji, chairman of Wipro ($8 billion)5) Charles Francis Feeney, co-founder of Duty Free Shoppers Group ($6.3 billion)6) Sulaiman bin Abdul Aziz Al Rajhi, cofounder of Al Rajhi Bank ($5.7 billion)7) Gordon Moore, co-founder of Intel ($5 billion)8) Carlos Slim Helu a Mexican telecom tycoon9) Eli Broad, co-founder of KB Home ($3.3 billion)10) George Kaiser, chairman of BOK Financial Corporation ($3.3 billion)11) Michael Bloomberg, founder of Bloomberg LP ($3 billion)12) Paul Allen, co-founder of Microsoft ($2 billion)13) Mark Zuckerberg, founder of Facebook ($1.6 billion)14) Li Ka-shing, chairman of CK Hutchison Holdings ($1.4 billion)15) Jon Huntsman Sr, founder of Huntsman Chemical Corporation ($1.2 billion)16) Ted Turner, founder of CNN ($2.1 billion)17) James Simons, a hedge fund manager ($1.2 billion)18) Michael Dell, founder of Dell ( $1.1 billion)19) Pierre Omidyar, co-founder of eBay ($1 billion)20) Dietmar Hopp, co-founder of SAP ($1 billion)(Source: Wealth-X)