Alan Boal, 58, said greed drove him to defraud Vallourec Oil and Gas UK over a five year period while he was employed as its chief financial controller.
Boal submitted false expenses forms, claimed for mileage on days when he was not working and bought gifts including Christmas presents for his family using the company credit card.
He was caught after a colleague became suspicious and kept a record of his inflated claims.
Boal, of Paisley, Renfrewshire, was investigated by bosses at the firm. Police were called in and he confessed to the scam.
At Hamilton Sheriff Court he admitted defrauding the company of £80,000 by making false expenses claims between May 2008, and January 2013.
Fiscal depute Imran Bashir told the court: "At the time of the commission of these offences the accused was regarded as one of the top financial controllers in the company.
"Several senior managerial staff within the company were issued with credit cards which were used for business related expenses such as hotel stays and business lunches.
"In January 2013, a witness attended the HR department and reported the accused as having submitted false expenses. He said he had been suspicious of the accused for some time but as the accused was his boss he had been afraid of reporting the matter."
The company, which supplies steel pipes to the oil and gas industry, decided to call in police and Boal confessed to colleagues during a meeting at the Dakota Hotel in Motherwell, North Lanarkshire.
Mr Bashir added: "The accused said 'I've let you down, I'm really sorry. I don't know why I did it, I suppose it was just greed. It probably culminated in me buying Christmas presents for my family with the company credit card and I accept they are not business related'.
"When one of the witnesses said to the accused 'This has been going on for a long, long time,' he replied: 'Yes, but probably over the last 12 months or so the amount has been more than what was taken previously'."
Mr Bashir also told the court that many of the expenses claims were for times when Boal was on leave. He added: "He wasn't working during those periods and there were other times when he failed to submit appropriate expenses forms and used the company credit card for non-business related activity."
Management at Vallourec called in PricewaterhouseCoopers to carry out an analysis of Boal's expenses forms.
Boal, who was based at the company's site in Bellshill, North Lanarkshire, was originally charged with defrauding the firm of £197,465 but pled guilty to the reduced amount. The court heard he had paid back £100,000.
Sheriff Joyce Powrie deferred sentence on Boal until next month for background reports and continued his bail.