It is now clear that the disastrous Deepwater Horizon oil spill was eminently preventable. And even since the April 20 rig fire, experts have cited many examples of how poor choices by BP have worsened an already dire situation. Here are eight particularly unfortunate errors that experts say contributed to the biggest oil spill in U.S. history:

1. BP never had a realistic plan to deal with a spill
The oil giant's official plan for dealing with a potential Deepwater Horizon spill, and its more general plan for any spill in the Gulf, both wildly overestimated its preparedness and seriously lowballed the potential damage, according to an AP analysis. The plan — approved by the Interior Department in 2009 — lists a dead scientist among its wildlife experts and a defunct Japanese home-shopping website among its equipment suppliers. Portions of it are written in pencil.

2. BP went with a risky type of blowout preventer — and then didn't maintain it
The blowout preventer is a giant valve that is supposed to be the last line of defense against a damaged well becoming an ecological catastrophe. But for the Deepwater Horizon project, BP chose a model — made by U.S.-based Cameron International — with well-documented design flaws. To make matters worse, according to a congressional investigation, the Deepwater's blowout preventer was in terrible shape: It had a dead battery, debilitating hydraulic-system leaks, and "shutoff shears" that weren't strong enough to seal the well. BP also opted not to install a voluntary $500,000 acoustic shutoff switch that could have sealed the well by remote control in the event the blowout preventer failed, reports the WSJ.

3. The well's critical plumbing was shoddy and poorly designed
Days before the blowout, BP decided to use a type of single-wall well casing that it knew increased the risk of gas leaks like the one that ultimately caused the deadly fire on the rig, according to The New York Times. Why? To save money. Drilling experts also say that BP's design for the casing pipe from the sea floor to the oil reservoir has a baffling design flaw that made it essentially impossible to create effective cement seals, the primary guards against natural gas leaks.

4. BP and rig workers ignored or misread clear warning signs
As Halliburton contractors were lowering the final cement plug down the well, rig workers conducted several tests for gas leaks — and in what an internal BP postmortem calls a "fundamental mistake" — they misinterpreted a "very large abnormality." When they decided, wrongly, that the test results were acceptable, they replaced the heavy drilling mud in the well with lighter seawater, allowing the pockets of natural gas below to explode upward and, ultimately, set the rig ablaze.

5. A "company man" overrode explosion concerns of well cementers
BP sent home the contractor it had hired to test the cement plug inside the well 11 hours before the explosion, without ever having him conduct the "gold standard" test on whether the seal was secure, according to the testing firm. A BP "company man" also overruled other safety concerns, including replacing the drilling mud with seawater, says another partner company. 

6. BP hasn't fessed up about how much oil is really spilling
Experts tend to agree that, in order to prepare for containment and cleanup efforts, federal and state officials need to know how much oil they're dealing with. But the oil company has been slippery on that point: BP said two days after the explosion that no oil was leaking; three days later, it said 1,000 barrels per day (bpd) were leaking; three days after that, it was 5,000 bpd — even after a "confidential" company memo said that up to 14,266 bpd was gushing out. BP no longer gives estimates, but government scientists Thursday said the true leak rate is has been between 20,000 to 40,000 bpd.

7. BP's "solutions" may be making the spill much, much worse
The company's string of failed attempts to seal or contain the leak — top hat, top kill, junk shot — may, in fact, be intensifying the problem. A flow-rate expert on the government panel looking into the leak rate, Dr. Ira Leifer of the University of California at Santa Barbara, says that both the top kill and containment cap strategies have damaged the well and dramatically increased the amount of oil spurting into the ocean. He suggests that, following BP's decision to install a containment cap, the leak may now be 100,000 barrels per day.

8. BP needs a bigger boat
While the containment cap strategy may have made the overall situation worse, the company is finally collecting sizable quantities of oil from the wellhead. The problem? There's no place to store it all, reports the WSJ. The tanker now floating above the wellhead can process about 18,000 barrels per day, while BP has a stated goal of collecting 50,000 bpd. The company is scrambling to bring in more ships, and will begin burning off as much as possible.