As we have been advising our 24/7 Wall St. readers, when the earnings reporting season comes to an end, the windows for insiders at major U.S. companies to make transactions will open back up. They did just that with a flurry of activity last week. We saw some of the highest insider buying and selling of the entire spring, and we would expect it to continue through May and June.

We cover insider buying each and every week at 24/7 Wall St., and we like to remind readers that while insider buying is usually a very positive sign, it is not in and of itself a reason to run out and buy a stock. Sometimes insiders and 10% owners have stock purchase plans set up at intervals to add to their holdings. That aside, it still remains an overall positive indicator.

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Here are some of the companies that reported notable insider buying last week.

Western Refining Inc. (WNR) hit our screens for the second week in a row as another insider make a sizable purchase of the stock. The chairman of the company bought a large 500,000-share block of shares at prices that ranged from $21.53 to $21.80 apiece. The total for the purchase came to $11 million. The company operates as an independent crude oil refiner and marketer of refined products. Its shares traded on Friday's close at $23.23, so the timing looks very solid.

Sotheby’s (BID) had two people high up in the company buying shares. The chief financial officer (CFO) and a director at the company bought a total of 64,000 shares at prices that ranged from $27.49 to $28.40. The total for the purchase was posted at $2 million. Sotheby's operates as an auctioneer of authenticated fine art, decorative art, jewelry, wine and collectibles in the United States, the United Kingdom, China, France, Switzerland, and elsewhere. The stock closed Friday at $28.65.

Hertz Global Holdings Inc. (HTZ) has struggled terribly over the past year, and shareholders may be pleased to know that the chief executive, CFO and an executive vice president of the rental car giant all bought shares last week. The trio acquired a total of 171,000 shares of the stock at prices between $7.63 and $7.85 per share. The total for the buy was posted at $1 million. Hertz ended last week at $8.70, so here too the timing looks solid.

American Airlines Group Inc. (AAL) had a director at the firm picking up shares this past week. The director purchased some 35,000 shares of the airline at $31.79 per share. The total for the buy was $1 million. The company operates 946 mainline aircraft, as well as 587 regional aircraft through regional airline subsidiaries and third-party regional carriers. It serves 350 destinations in approximately 50 countries. The shares closed Friday at $32.01, so perhaps another bottom tick, as the stock has been hit pretty hard since late in 2015.