Estimates of Saudi spending on religious causes abroad include "upward of $100 billion";[272] $2–3 billion per year since 1975 (compared to the annual Soviet propaganda budget of $1 billion/year);[273] and "at least $87 billion" from 1987 to 2007.[274] Reliability of these rough estimates have been disputed due to their inconsistencies and lack of a scientific methodology for precise quantification.[275]

Its largesse funded an estimated "90% of the expenses of the entire faith", throughout the Muslim world, according to journalist Dawood al-Shirian.[276] It extended to young and old, from children's madrasas to high-level scholarship.[277] "Books, scholarships, fellowships, mosques" (for example, "more than 1,500 mosques were built from Saudi public funds over the last 50 years") were paid for.[278] It rewarded journalists and academics, who followed it and built satellite campuses around Egypt for Al Azhar, the oldest and most influential Islamic university.[279] Yahya Birt counts spending on "1,500 mosques, 210 Islamic centres and dozens of Muslim academies and schools".[273][280] Apart from state patronage, a major source of proselytization has been the private charities and religious activities of Muslim individuals and organizations.[281]

This financial aid has done much to overwhelm less strict local interpretations of Islam, according to observers like Dawood al-Shirian and Lee Kuan Yew,[276] arguing that it caused the Saudi interpretation (sometimes called "petro-Islam"[282]) to be perceived as the correct interpretation – or the "gold standard" of Islam – in many Muslims' minds.[283][284]

Peter Mandaville asserts that the commonly reported data estimates regarding Saudi religious funding are unreliable due to the sources being "internally inconsistent" and based on "non-specific hearsay". According to Mandaville, the wide-ranging and controversial usage of the term "Wahhabism" has rendered researching Saudi religious transnationalism and assessing its actual magnitude even more confusing. Moreover, the post-Cold War era governments had commonly used the label "Wahhabism" to designate a wide swathe of religious sects, including those which were doctrinally at odds with Wahhabism.[275]