How to spend $5 trillion: a record-breaking year in deals

Low interest rates since the Great Recession have made it cheaper for companies to borrow money to pay for acquisitions, and because the global economy only grew slowly this year, companies decided it made more sense to buy their competitors instead of trying to boost their sales on their own.

Oil and gas company Shell agreed to buy BG Group for $69.83 billion to expand its liquid natural gas business.

Natural gas prices have tumbled since then, and in December they reached their lowest levels in 16 years.

Dell's personal computer sales have been weak for years, but the company has been expanding its software and service businesses.

When the $62.38 billion deal closes, Dow DuPont will make products including Ziploc bags, Saran wrap, Teflon coatings and Nylon and Kevlar fibers.

A wave of health insurance combinations swept the market in July as Anthem announced it would buy Cigna for $51.93 billion just after Aetna said it would buy Humana for $35.04 billion.

Anthem sells health coverage to individuals and employees of small businesses and serves Medicare, Medicaid and federal employees.

Investors value PayPal more highly than its former parent, as PayPal has a market capitalization of about $45 billion compared to eBay's $33 billion.