OMAHA, Neb. (AP) — Billionaire Warren Buffett says his company has benefited from some “extraordinary luck” in finding acquisitions like BNSF railroad over the decades, but he hasn’t had much of that in recent years as Berkshire Hathaway’s cash pile has grown to nearly $147 billion.

Buffett sought to reassure shareholders with his annual letter Saturday that he retains a strong appetite for acquisitions and stock investments, but he hasn’t found many of either that interest him at today’s inflated prices.

He blamed the continued low interest rates for helping drive up the price of stocks and whole companies alike, and in the past he has said that increasing competition from private equity buyers has made it hard to find good deals.

“From time to time, such possibilities are both numerous and blatantly attractive. Today, though, we find little that excites us,” Buffett wrote about the prospects for finding good stock investments.

Berkshire has focused on growing the 90-odd businesses the Omaha, Nebraska-based conglomerate already owns and repurchasing its own shares — something Buffett has invested $51.7 billion in over the last two years including $27 billion last year.

And despite the dearth of acquisitions and new investments Berkshire has continued to profit. The company reported making $39.6 billion, or $26,690 per Class A share, during the fourth quarter. That’s up from $35.8 billion, or $25,015 per Class A share, a year ago.

But those bottom line figures were inflated by paper gains on Berkshire’s investments, which is why Buffett maintains that operating earnings are a better measure of the company’s performance because they exclude investments and derivatives. By that measure, Berkshire’s operating earnings jumped from $5.02 billion, or $3,224.74 per Class A share, to $7.3 billion, or $4,904.23 per Class A share, during the fourth quarter.

The four analysts surveyed by FactSet expected Berkshire to report operating earnings per Class A share of $4,197.84 in the quarter.

Berkshire owns an eclectic variety of companies, including BNSF, a number of large electric utilities, Geico insurance and an assortment of manufacturing and retail companies. The conglomerate also holds large stock investments in Apple, Coca-Cola, Bank of America and other companies.