After university Siebens served in the United States Air Force for three years as a pilot.

When his term in the Air Force was completed in 1958, Siebens moved to Calgary, Alberta, where his parents had relocated.

In February 1965 he sold controlling interest in the company to Canadian Export Gas and Oil Limited.

"[5] The deal involved the purchase of Siebens for $38.50 per share, or a total value of $360 million, by the Canadian National Railways pension fund via a subsidiary called Canpar Oil and Gas Limited.

Through its status as a pension fund subsidiary, Canpar was exempted from paying taxes on the sale to Dome.

[7] On 22 May 1961, Siebens married Clarice Adrienne Evans at Rundle United Church in Banff, Alberta.