The ECB is governed by European law directly, but its set-up resembles that of a corporation in the sense that the ECB has shareholders and stock capital. Its initial capital was supposed to be €5 billion and the initial capital allocation key was determined in 1998 on the basis of the member states' populations and GDP, but the key is adjustable. The euro area NCBs were required to pay their respective subscriptions to the ECB's capital in full. The NCBs of the non-participating countries have had to pay 7% of their respective subscriptions to the ECB's capital as a contribution to the operational costs of the ECB. As a result, the ECB was endowed with an initial capital of just under €4 billion. The capital is held by the national central banks of the member states as shareholders. Shares in the ECB are not transferable and cannot be used as collateral. The NCBs are the sole subscribers to and holders of the capital of the ECB.