Quoting Lukas Rech: "I am trying to do some work on CDS im my bachelor thesis. Therefore, I downloaded stock price data from DataStream and transformed the data such that in the first column is a variable that represents the time dimension as well as the firm codes, which are numbers from 9 to 4631. These numbers are firm tickers from a dataset of CDS spreads, which I want to append with my stock price data. The CDS data can be read in perfectly as panel data, but Gretl wont let the .xlsx file to be interpreted as panel. "Does anyone have an idea, what I am doing wrong and how I could transform my data, such that Gretl can recognice the panel data structure?" Lukas's data file was too big too post to the list, but I've taken a look at it myself and the answer is quite simple. One check gretl does when you try to define a dataset as a panel via index variables is that it counts the distinct values of the unit and time variables, finds the product of these counts (call it 'P'), and compares it with the total number of observations, N. If P < N that means that the unit and time variables do not jointly provide unique ID for the observations: somewhere in the dataset there must be at least two observations sharing the same unit and time values, so it's malformed as a panel. In Lukas's case it turns out to be just the first two observations, both of which have Time = 730908 and MapNum (unit) = 9. Delete one of those rows and the data will be read as a panel OK. (In gretl CVS I've now made the error message for this sort of case more informative.) Allin Cottrell