Oil shale in Israel is widespread but an undeveloped resource, largely because of economic and technological constraints. Israeli oil shales belong to the group of Upper Cretaceous marinite deposits. Although oil-shale deposits may lie under as much as 15% of the country, only a small part of these are mineable. According to the Geological Survey of Israel, deposits that could have the biggest economic potential are located in the northern Negev, the largest being the Rotem-Yamin formation. For several decades, oil shale was used for small-scale power generation at Mishor Rotem. Several Israeli companies have proposed shale oil extraction; testing of the viability of the oil shale industry is currently being undertaken by Israel Energy Initiatives. However, as of 2011, there are no commercial oil shale operations in Israel.