(11)The need for clarification is particularly pressing for derivatives on financial indices. There is currently a wide range of financial indices which function as the underlying for a derivative instrument. These indices may vary as regards their composition or the weighting of their components. In all cases it has to be ensured that the UCITS is able to fulfil its obligations as regards portfolio liquidity, as resulting from Article 37 of Directive 85/611/EEC, and the calculation of the net asset value and that those obligations are not negatively affected by the features of the underlying of a derivative. It should be clarified that derivatives on financial indices whose composition is sufficiently diversified, which represent an adequate benchmark to the market to which they refer and which are subject to appropriate information regarding the index composition and calculation fall under the category of derivatives as liquid financial assets. National competent authorities could work together through the CESR to develop common approaches as regards the practical, day-to-day application of those criteria in respect of indices based on assets which are not individually identified as eligible assets in the Directive.