// In C# 3.0 and earlier versions, you need to supply an argument for // every parameter. The following call specifies a value for the first // parameter, and sends a placeholder value for the other six. The // default values are used for those parameters. var excelApp = new Microsoft.Office.Interop.Excel.Application(); excelApp.Workbooks.Add(); excelApp.Visible = true; var myFormat = Microsoft.Office.Interop.Excel.XlRangeAutoFormat.xlRangeAutoFormatAccounting1; excelApp.get_Range("A1", "B4").AutoFormat(myFormat, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);