From 2018, all licences are governed by Revenue/Cost index (R/C) production sharing contracts. Contracts are awarded through direct negotiation or during a licensing round. The R/C index based sliding scales for cost recovery ceilings, sharing of unused cost oil and profit oil are set prior to each licensing round and are non-biddable items. Other non-biddable items include an export duty of 10%, a research contribution of 0.5%, a sliding scale based supplementary payment of 50 to 70% and petroleum income tax of 38%. In 2010, a range of incentives was introduced to promote investments in the upstream sector, including the additional income tax allowance for deepwater areas.