About 75% of the inland business is under contract, a year or longer in duration, 55% of that is time charter. On the coastal side of the business, about 60% of the business is under contract and 90% of that is time charter. Our diesel engine service area, an area that we've expanded significantly last year, has a national footprint. It is in the service, distribution and parts business for medium and high-speed engines. It also manufactures or assembles equipment for oil service work, principally for land based applications. On the manufacturing side it's making these high-pressure hydraulic fracking pumps, cementers, nitrogen systems, that kind of equipment.
Kirby has been a consolidator in the industries that it's in, an aggregation in total of about 45 separate acquisitions. This lists the marine acquisitions. Most of these you won't recognize other than the shipper fleets that we bought, Exxon, Dow, Union Carbide, those types of fleets. And then the activity in the diesel engine business, the last was by far the biggest, United Holdings located in Oklahoma City.
We've enjoyed strong revenue growth. This revenue growth goes back into the late 80s, since 1988 over 16% compounded on an annual basis and then with respect to earnings per share, 15% of earnings growth. Now, moving to the marine transportation business. This is the kind of the areas that we operate. We operate on the inland waterway system of the United States; 12,000 miles of navigable waterways. There isn't a system like the inland waterway system anywhere in the world.
About 80% of the chemicals in the United States are manufactured in two states, Texas and Louisiana. And on a total transportation basis about 60% of what we do is in the chemical area. So about two-thirds of our inland fleet is heavily concentrated in the Texas, Louisiana area, and the rest of it is up on the Mississippi river and its tributaries. And then with respect to our costal fleet, KC transportation has the largest geographical footprint. It operates on the three coasts and it also has operations in Hawaii and Alaska.