Hamas terrorists in Gaza
Hamas terrorists in GazaReuters

ISIS may still be the world's richest terror organizations, Forbes Israel revealed Tuesday - but Hamas is a close second. 

Terror groups require an enormous amount of resource and financial capital to carry out attacks, the financial group noted - but are forced to take their assets through physical conquest, backroom deals, or the black market. 

Alongside the criminal activity par excellence, there are also public donations or transactions with terror organizations, it noted.

Huge amounts of money are transferred to terror groups by non-profit organizations, charities, businesses and financial institutions - and even some governments. 

The transactions not only legitimize terror and provide funds for further attacks, but has become an important issue in light of ISIS's stranglehold on the Middle East and Hamas's recent pact with the Palestinian Authority (PA). 

Forbes's list of the top 10 richest terror organizations are as follows: 

According to Forbes, ISIS tops the list with a $2 billion annual income and is the world's richest terrorist organization - and the richest in the history of modern terrorism. 

Experts estimate that ISIS currently controls 60% of oil reserves in Syria, and was able to take by force or negotiate with the seven major oil and gas reserves in Iraq, including the country's largest oil refinery. ISIS ultimately sells tens of thousands of barrels of oil on the black market daily, and the fossil fuel is a huge cash cow for the organization. The oil is sold at 40% to 75% less than the market price, yet the organization manages to pocket every day an estimated three million dollars for the sales.

Hamas is the second-richest terror organization, Forbes said, with about $1 billion being funneled to the terror group annually. 

Since taking over Gaza in 2007, Hamas has made the big leagues: in less than a decade, Hamas managed to turn the organization - which relies mainly on NGO funds and foreign aid - into a multilevel organization which also governs, and taxes, Gaza. And the taxes are high, according to Walla! News: all car owners are required to pay Hamas 1,400 shekel (about $366) annually for a licensing fee, and gas stations are heavily taxed. Much of Hamas's income, however, is from foreign aid and NGOs - and may be a major factor in Israel's security after the multibillion-dollar donations made from the UN and other countries after the summer's war.