X0202 4 2006-08-31 1 0000075129 OTTER TAIL CORP OTTR 0001191502 SPOLUM ROBERT N 215 S CASCADE ST FERGUS FALLS MN 56537-2801 0 0 0 1 No longer Subject to Section 1 Common Stock 2006-08-31 4 S 0 1715 30.13 D 21130 D Common Stock 2006-08-31 4 S 0 600 30.14 D 20530 D Common Stock 2006-08-31 4 S 0 400 30.16 D 20130 D Common Stock 2006-08-31 4 S 0 500 30.17 D 19630 D Common Stock 2006-08-31 4 S 0 510 30.25 D 19120 D Common Stock 2006-08-31 4 S 0 100 30.26 D 19020 D Common Stock 2006-08-31 4 S 0 100 30.28 D 18920 D Common Stock 2006-08-31 4 S 0 690 30.29 D 18230 D Common Stock 2006-08-31 4 S 0 100 30.30 D 18130 D Common Stock 2006-08-31 4 S 0 100 30.31 D 18030 D Common Stock 2006-08-31 4 S 0 185 30.33 D 17845 D These shares are held in "street name" with Merrill Lynch. See below for other holdings: 1. 2,000 stock options with expiration date of 4/8/2011. Mr. Spolum is under the six month obligation period for this sale as he retired from the Board of Directors as of April 10, 2006. /s/ Robert N Spolum by Debra J Lill -POA 2006-08-31