The New York Stock Exchange is looking at irregular trading in the stock of 140 companies, a substantial chunk of the more than 2,800 tickers listed on the world's most prominent bourse, after a morning filled with bizarre market action that at least one market analyst is dubbing "flash crash epic," a reference to the infamous late-afternoon market collapse of May 6, 2010.

At 10:41 a.m. EDT, exchange operator NYSE Euronext sent out a notice to traders that it was conducting a "clear execution error review" on trading between 9:30 and 10:15 a.m. That notice followed a morning filled with wild trading patterns, with shares in various companies inexplicably dropping or rising by over 5 percent -- or trading at over 40 times usual volume -- on no apparent news.

Usually thinly traded issues swung up and down in uncharacteristic manner while posting impossibly high volumes.

Fully 52 issues traded at a higher volume than the heavily traded tracking ETF for the S&P 500 (NYSEARCA: SPY), something that Eric Scott Hunsader, chief executive at market data analysis firm Nanex LLC says "never happens," since "SPY is always, or almost always the most traded."

Hunsader's research firm put together a list of 113 stock symbols that saw unusual volume Wednesday, which is reproduced below, and could give a good sense of the companies affected. They include Finnish cellphone maker Nokia Corporation (NYSE:NOK), tiremaker Goodyear Tire and Rubber Company (NYSE:GT), motorcycle manufacturer Harley-Davidson Inc. (NYSE:HOG), electronics retailer RadioShack Corporation (NYSE:RSH), online broadcaster Pandora Media Inc. (NYSE: P) and healthcare products provider Allergan Inc. (NYSE:AGN), all of which saw massive swings in their share prices close to or over 10 percent.

ExchangeSymbolNameNumber of TradesTotal Volume
NYSEeNOKNOKIA239,34923,204,514
NYSEeJNPRJUNIPER NETWORKS168,86520,977,149
NYSEeBACBANK of AMERICA125,41424,103,441
PACFeUNGUNITED STATES NATURAL GAS112,00416,591,565
NYSEeFFORD MOTOR109,40820,068,766
PACFeNUGTDIREXION DAILY GOLD MINERS BUL107,51213,345,640
NYSEeAAALCOA102,67212,273,467
NYSEeLOWLOWES COMPANIES92,94910,570,989
NYSEeCCITIGROUP91,32313,301,431
NYSEeSDSANDRIDGE ENERGY82,38311,172,033
NYSEeLSILSI81,07612,265,065
NYSEeGLWCORNING80,15214,228,151
NYSEeWFCWELLS FARGO70,93510,766,506
NYSEePFEPFIZER66,99510,341,023
NYSEeBBYBEST BUY60,2386,566,346
NYSEeLADLITHIA MOTORS58,6626,129,476
NYSEeEXCEXELON58,2656,411,808
NYSEeGNWGENWORTH FINANCIAL57,53110,873,685
NYSEeAMTAMERICAN TOWER56,8656,062,697
NYSEeKGCKINROSS GOLD55,61710,134,667
NYSEeWLPWELLPOINT55,1315,813,227
NYSEeEXGEATON VANCE TAX-MANAGED GLOBAL52,1805,824,742
AMEXeNGNOVAGOLD RESOURCES50,1386,419,751
NYSEeACIARCH COAL47,3408,534,900
NYSEeAMTDTRADE AMERITRADE HOLDINGS45,4505,798,959
NYSEeDEDEERE43,2235,283,885
NYSEeANRALPHA NATURAL RESOURCES42,2777,186,454
NYSEePGHPENGROWTH ENERGY41,9445,161,389
NYSEeNVSNOVARTIS41,3685,117,031
NYSEeMTWMANITOWOC40,9305,532,452
AMEXeLNGCHENIERE ENERGY40,6815,232,434
NYSEeGTGOODYEAR TIRE & RUBBER40,6245,893,403
NYSEeBGBUNGE40,5224,987,540
PACFeGDXMARKET VECTORS GOLD MINERS ETF40,0547,672,185
NYSEeCOHCOACH40,0375,349,251
NYSEeGMGENERAL MOTORS39,9245,613,714
NYSEeDDEI DU PONT DE NEMOURS39,8554,996,331
NYSEeHOGHARLEY-DAVIDSON39,8375,093,204
NYSEeGGGOLDCORP39,6394,757,447
NYSEeSWNSOUTHWESTERN ENERGY39,5934,697,193
AMEXeREERARE ELEMENT RESOURCES39,0404,571,278
NYSEeARRARMOUR RESIDENTIAL REIT38,8456,413,554
NYSEePEPPEPSICO38,6875,077,333
NYSEeRSHRADIOSHACK38,5326,244,358
NYSEeJWNNORDSTROM37,5114,340,214
NYSEeAUYYAMANA GOLD37,4114,926,084
NYSEeBRK.BBERKSHIRE HATHAWAY36,9404,685,130
NYSEeKWKQUICKSILVER RESOURCES36,9185,177,516
NYSEePPANDORA MEDIA36,6884,532,103
NYSEeAGNALLERGAN36,4914,420,354
NYSEeMPCMARATHON PETROLEUM36,4144,468,685
PACFeSPYSPDR S&P 50035,85113,192,353
NYSEeANFABERCROMBIE & FITCH35,7884,540,535
NYSEeGOVGOVT PROPERTIES35,6864,315,824
NYSEeTSMTAIWAN SEMICONDUCTOR34,6076,108,790
NYSEeCVSCVS CAREMARK34,4814,506,898
NYSEeAMDADVANCED MICRO DEVICES34,3365,470,129
NYSEeTKRTIMKEN33,8514,193,885
NYSEeAFLAFLAC33,8194,163,863
NYSEePIRPIER 1 IMPORTS33,7304,045,445
NYSEeBUDANHEUSER-BUSCH INBEV33,6104,341,290
NYSEeVZVERIZON COMMUNICATIONS33,3425,225,744
NYSEeNATNORDIC AMERICAN TANKERS32,9954,238,036
NYSEeTRNTRINITY INDUSTRIES32,6093,859,581
NYSEeTWOTWO HARBORS INVESTMENT32,5245,718,226
NYSEeDOWDOW CHEMICAL32,1793,981,096
NYSEeMCPMOLYCORP32,0944,368,593
NYSEeJWFWELLS FARGO CAPITAL IX 5.625%31,9223,677,023
NYSEeCODESPANSION31,9043,718,209
AMEXeEADWELLS FARGO ADVANTAGE INC OP31,7743,692,158
NYSEeHUMHUMANA31,7573,906,305
NYSEeHFCHOLLYFRONTIER31,6964,050,147
NYSEeGMEGAMESTOP31,5143,895,044
NYSEeDOLEDOLE FOOD31,2533,763,344
NYSEeMHRMAGNUM HUNTER RESOURCES31,1734,746,265
NYSEeHLFHERBALIFE31,0774,037,442
NYSEePLPROTECTIVE LIFE30,1963,338,214
NYSEeUNUNILEVER29,8963,848,343
NYSEeLVLTLEVEL 3 COMMUNICATIONS29,8433,688,276
NYSEeHMCHONDA MOTOR29,7083,367,606
NYSEeMTZMASTEC29,5283,570,217
NYSEeNNETSUITE29,4963,493,153
NYSEeFSLFREESCALE SEMICONDUCTOR29,2193,511,255
NYSEeSANSANTANDER FINANCE SA UNIPERSON28,5254,139,607
NYSEeARCAMERICAN REPROGRAPHICS27,4752,984,143
NYSEeBYDBOYD GAMING27,1473,251,515
NYSEeFRXFOREST LABORATORIES26,6773,287,709
AMEXeNAVBNAVIDEA26,6693,903,983
NYSEeULUNILEVER26,6443,323,404
NYSEeDDD3D SYSTEMS25,5002,998,497
NYSEeEJE-HOUSE CHINA HOLDINGS23,2472,720,709
AMEXeCFPCORNERSTONE PROGRESSIVE RETURN21,8052,475,916
NYSEeNEMNEWMONT MINING20,0832,412,260
NYSEePSXPHILLIPS 6612,1501,999,847
NYSEePPOPOLYPORE INTL10,7782,203,496
AMEXeLODECOMSTOCK MINING7,643825,705
NYSEeKCGKNIGHT CAPITAL GROUP7,3801,727,987
NYSEeOCOWENS-CORNING6,7881,117,712
NYSEeRBS.PR.FROYAL BANK of SCOTLAND6,042682,001
AMEXeNGDNEW GOLD5,153808,907
NYSEeIAGIAMGOLD4,901865,563
NYSEeHMYHARMONY GOLD MINING CO4,172689,191
NYSEeHBIHANESBRANDS3,639777,936
NYSEeBVNBUENAVENTURA MINING3,632510,324
NYSEeNUSNU SKIN ENTERPRISES3,584511,533
NYSEeWNCWABASH NATIONAL3,481712,752
NYSEeRDNRADIAN GROUP3,4271,250,856
NYSEeCNWCON-WAY3,266504,774
NYSEeCLGXCORELOGIC3,200420,942
NYSEeRATEBANKRATE2,707467,748
NYSEeDGIDIGITALGLOBE2,569542,286
NYSEeRFPRESOLUTE FOREST PRODUCTS2,423649,848
NYSEeICEINTERCONTINENTALEXCHANGE1,627247,439
NYSEeMTORMERITOR1,585479,808

Rich Adamonis, a spokesman for the exchange, said the review was still underway but that it had been at least ascertained that "the systems were working properly."

That assertment did not inspire a lot of confidence in the market around lunchtime, as rumors swirled that the unusual market action was coming out of market-maker.

"I think this is a systems failure," Hunsader said, noting the way a large volume of trades were marked as "regular" trades suggested a tertiary market-maker had inadvertently been allowed to inundate the market with a slew of orders, perhaps in a ham-fisted attempt to try out a new trading strategy. Hunsafer and others speculated it could all be related to the introduction of the Retail Liquidity Program, a "dark pool" trading platform that went online Wednesday morning.

"It looks like somebody hooked up and maybe mucked up," Hunsader said.

Many fingers were being pointed at market-maker Knight Capital Group Inc. (NYSE: KCG), though it is not year clear they were exclusively to blame for the unusual market action. In a statement, that company noted that "an initial review by Knight indicates that a technology issue occurred in the company's market-making unit related to the routing of shares of approximately 150 stocks to the NYSE. Knight notified its market-making clients this morning to route listed orders away."

Knight shares were down about 22 percent in afternoon trading.

Joe Saluzzi, a partner at New Jersey-based Themis Trading, who has been highly critical in the past of the effect of algorithm-focused trading in the market, said what he termed the "flash smash" was likely the result of "a rogue algorithm wreaking havoc on the market."

"This is a market structure failure," Saluzzi said, "The equity market has been hollowed out some time now. When you have a market like that, you're going to have events like this, where everything is going crazy when no one knows what's going on."

By mid-afternoon, it seemed the markets had stabilized, but there were still many questions on the table. It was not clear how many investors had been affected by the market action, but Saluzzi noted he couldn't "even imagine how many stop loss orders were unnecessarily triggered today and how much money investors lost today."

"What you're going to hear is that it was a technical event and everything is fixed now. Unfortunately, people are getting hurt," he said.